diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/AbstractDependentCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/AbstractDependentCell.kt
index 6b3a42f5..0aa62026 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/AbstractDependentCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/AbstractDependentCell.kt
@@ -2,7 +2,7 @@ package world.phantasmal.cell
 
 import world.phantasmal.core.unsafe.unsafeCast
 
-abstract class AbstractDependentCell<T, Event : ChangeEvent<T>> : AbstractCell<T>(), Dependent {
+internal abstract class AbstractDependentCell<T, Event : ChangeEvent<T>> : AbstractCell<T>(), Dependent {
 
     protected var _value: T? = null
     final override val value: T
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/AbstractFlatteningDependentCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/AbstractFlatteningDependentCell.kt
index 50a7eca8..6051907f 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/AbstractFlatteningDependentCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/AbstractFlatteningDependentCell.kt
@@ -2,7 +2,7 @@ package world.phantasmal.cell
 
 import world.phantasmal.core.unsafe.unsafeAssertNotNull
 
-abstract class AbstractFlatteningDependentCell<T, ComputedCell : Cell<T>, Event : ChangeEvent<T>>(
+internal abstract class AbstractFlatteningDependentCell<T, ComputedCell : Cell<T>, Event : ChangeEvent<T>>(
     private val dependencies: Array<out Cell<*>>,
     private val compute: () -> ComputedCell,
 ) : AbstractDependentCell<T, Event>() {
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/CallbackChangeObserver.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/CallbackChangeObserver.kt
index 258ec491..1d2a82bd 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/CallbackChangeObserver.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/CallbackChangeObserver.kt
@@ -6,7 +6,7 @@ import world.phantasmal.core.unsafe.unsafeCast
 /**
  * Calls [callback] when [dependency] changes.
  */
-class CallbackChangeObserver<T, E : ChangeEvent<T>>(
+internal class CallbackChangeObserver<T, E : ChangeEvent<T>>(
     private val dependency: Cell<T>,
     // We don't use ChangeObserver<T> because of type system limitations. It would break e.g.
     // AbstractListCell.observeListChange.
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/CallbackObserver.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/CallbackObserver.kt
index bec61280..0237371f 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/CallbackObserver.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/CallbackObserver.kt
@@ -5,7 +5,7 @@ import world.phantasmal.core.disposable.TrackedDisposable
 /**
  * Calls [callback] when one or more cells in [dependencies] change.
  */
-class CallbackObserver(
+internal class CallbackObserver(
     private vararg val dependencies: Cell<*>,
     private val callback: () -> Unit,
 ) : TrackedDisposable(), LeafDependent {
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/DelegatingCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/DelegatingCell.kt
index 8f149af3..d86e4eaa 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/DelegatingCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/DelegatingCell.kt
@@ -1,6 +1,6 @@
 package world.phantasmal.cell
 
-class DelegatingCell<T>(
+internal class DelegatingCell<T>(
     private val getter: () -> T,
     private val setter: (T) -> Unit,
 ) : AbstractCell<T>(), MutableCell<T> {
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/DependentCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/DependentCell.kt
index 202f2f4a..9af0fbb1 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/DependentCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/DependentCell.kt
@@ -3,7 +3,7 @@ package world.phantasmal.cell
 /**
  * Cell of which the value depends on 0 or more dependencies.
  */
-class DependentCell<T>(
+internal class DependentCell<T>(
     private vararg val dependencies: Cell<*>,
     private val compute: () -> T,
 ) : AbstractDependentCell<T, ChangeEvent<T>>() {
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/FlatteningDependentCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/FlatteningDependentCell.kt
index 6c9effb1..83a6b52a 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/FlatteningDependentCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/FlatteningDependentCell.kt
@@ -3,7 +3,7 @@ package world.phantasmal.cell
 /**
  * Similar to [DependentCell], except that this cell's [compute] returns a cell.
  */
-class FlatteningDependentCell<T>(
+internal class FlatteningDependentCell<T>(
     vararg dependencies: Cell<*>,
     compute: () -> Cell<T>,
 ) : AbstractFlatteningDependentCell<T, Cell<T>, ChangeEvent<T>>(dependencies, compute) {
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/ImmutableCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/ImmutableCell.kt
index 7dbe8031..38b985dd 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/ImmutableCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/ImmutableCell.kt
@@ -3,7 +3,7 @@ package world.phantasmal.cell
 import world.phantasmal.core.disposable.Disposable
 import world.phantasmal.core.disposable.nopDisposable
 
-class ImmutableCell<T>(override val value: T) : Dependency<T>, Cell<T> {
+internal class ImmutableCell<T>(override val value: T) : Dependency<T>, Cell<T> {
     override val changeEvent: ChangeEvent<T>? get() = null
 
     override fun addDependent(dependent: Dependent) {
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/SimpleCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/SimpleCell.kt
index 4a9229bd..08929b82 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/SimpleCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/SimpleCell.kt
@@ -1,6 +1,6 @@
 package world.phantasmal.cell
 
-class SimpleCell<T>(value: T) : AbstractCell<T>(), MutableCell<T> {
+internal class SimpleCell<T>(value: T) : AbstractCell<T>(), MutableCell<T> {
     override var value: T = value
         set(value) {
             if (value != field) {
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/AbstractFilteredListCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/AbstractFilteredListCell.kt
index fbea6e01..12feea2a 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/AbstractFilteredListCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/AbstractFilteredListCell.kt
@@ -5,7 +5,7 @@ import world.phantasmal.cell.Dependent
 import world.phantasmal.cell.MutationManager
 import world.phantasmal.core.unsafe.unsafeCast
 
-abstract class AbstractFilteredListCell<E>(
+internal abstract class AbstractFilteredListCell<E>(
     protected val list: ListCell<E>,
 ) : AbstractListCell<E>(), Dependent {
 
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/AbstractListCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/AbstractListCell.kt
index 1c64f58a..4cf644cb 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/AbstractListCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/AbstractListCell.kt
@@ -8,7 +8,7 @@ import world.phantasmal.cell.AbstractCell
 import world.phantasmal.cell.Cell
 import world.phantasmal.cell.DependentCell
 
-abstract class AbstractListCell<E> : AbstractCell<List<E>>(), ListCell<E> {
+internal abstract class AbstractListCell<E> : AbstractCell<List<E>>(), ListCell<E> {
 
     private var _size: Cell<Int>? = null
     final override val size: Cell<Int>
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/DependentListCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/DependentListCell.kt
index a9afd97a..05bf20a3 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/DependentListCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/DependentListCell.kt
@@ -7,7 +7,7 @@ import world.phantasmal.cell.Cell
 /**
  * ListCell of which the value depends on 0 or more other cells.
  */
-class DependentListCell<E>(
+internal class DependentListCell<E>(
     private vararg val dependencies: Cell<*>,
     private val computeElements: () -> List<E>,
 ) : AbstractListCell<E>(), Dependent {
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/FilteredListCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/FilteredListCell.kt
index 5412c62c..cb6c32bd 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/FilteredListCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/FilteredListCell.kt
@@ -8,7 +8,7 @@ import world.phantasmal.core.assert
 import world.phantasmal.core.assertUnreachable
 import world.phantasmal.core.unsafe.unsafeCast
 
-class FilteredListCell<E>(
+internal class FilteredListCell<E>(
     list: ListCell<E>,
     private val predicate: Cell<(E) -> Cell<Boolean>>,
 ) : AbstractFilteredListCell<E>(list) {
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/FlatteningDependentListCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/FlatteningDependentListCell.kt
index 29748f1a..d711644c 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/FlatteningDependentListCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/FlatteningDependentListCell.kt
@@ -9,7 +9,7 @@ import world.phantasmal.core.unsafe.unsafeAssertNotNull
  */
 // TODO: Improve performance when transitive cell changes. At the moment a change event is generated
 //       that just pretends the whole list has changed.
-class FlatteningDependentListCell<E>(
+internal class FlatteningDependentListCell<E>(
     vararg dependencies: Cell<*>,
     computeElements: () -> ListCell<E>,
 ) :
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/ImmutableListCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/ImmutableListCell.kt
index 8cfd17e6..f65273b2 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/ImmutableListCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/ImmutableListCell.kt
@@ -1,16 +1,13 @@
 package world.phantasmal.cell.list
 
+import world.phantasmal.cell.*
 import world.phantasmal.core.disposable.Disposable
 import world.phantasmal.core.disposable.nopDisposable
-import world.phantasmal.cell.ChangeObserver
-import world.phantasmal.cell.Dependency
-import world.phantasmal.cell.Dependent
-import world.phantasmal.cell.Cell
-import world.phantasmal.cell.cell
-import world.phantasmal.cell.falseCell
-import world.phantasmal.cell.trueCell
 
-class ImmutableListCell<E>(private val elements: List<E>) : Dependency<List<E>>, ListCell<E> {
+internal class ImmutableListCell<E>(
+    private val elements: List<E>,
+) : Dependency<List<E>>, ListCell<E> {
+
     override val size: Cell<Int> = cell(elements.size)
     override val empty: Cell<Boolean> = if (elements.isEmpty()) trueCell() else falseCell()
     override val notEmpty: Cell<Boolean> = if (elements.isNotEmpty()) trueCell() else falseCell()
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/ListCellUtils.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/ListCellUtils.kt
index 667dd0f9..e4613fce 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/ListCellUtils.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/ListCellUtils.kt
@@ -9,6 +9,10 @@ private val EMPTY_LIST_CELL = ImmutableListCell<Nothing>(emptyList())
 /** Returns an immutable list cell containing [elements]. */
 fun <E> listCell(vararg elements: E): ListCell<E> = ImmutableListCell(elements.toList())
 
+/** Returns a list cell backed by [elements]. */
+fun <E> listCell(elements: List<E>): ListCell<E> =
+    ImmutableListCell(elements)
+
 /** Returns a singleton empty immutable cell. */
 fun <E> emptyListCell(): ListCell<E> = EMPTY_LIST_CELL
 
@@ -16,6 +20,10 @@ fun <E> emptyListCell(): ListCell<E> = EMPTY_LIST_CELL
 fun <E> mutableListCell(vararg elements: E): MutableListCell<E> =
     SimpleListCell(mutableListOf(*elements))
 
+/** Returns a mutable list cell initially backed by [elements]. */
+fun <E> mutableListCell(elements: MutableList<E>): MutableListCell<E> =
+    SimpleListCell(elements)
+
 /**
  * Returns a cell that changes whenever this list cell is structurally changed or when its
  * individual elements change.
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/ListElementsDependentCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/ListElementsDependentCell.kt
index 6be66cc1..8426440c 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/ListElementsDependentCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/ListElementsDependentCell.kt
@@ -10,7 +10,7 @@ import world.phantasmal.cell.Cell
 /**
  * Depends on a [ListCell] and zero or more cells per element in the list.
  */
-class ListElementsDependentCell<E>(
+internal class ListElementsDependentCell<E>(
     private val list: ListCell<E>,
     private val extractCells: (element: E) -> Array<out Cell<*>>,
 ) : AbstractCell<List<E>>(), Dependent {
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/SimpleFilteredListCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/SimpleFilteredListCell.kt
index 7db2eff6..2de4631a 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/SimpleFilteredListCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/SimpleFilteredListCell.kt
@@ -4,7 +4,7 @@ import world.phantasmal.core.assertUnreachable
 import world.phantasmal.cell.Dependency
 import world.phantasmal.cell.Cell
 
-class SimpleFilteredListCell<E>(
+internal class SimpleFilteredListCell<E>(
     list: ListCell<E>,
     private val predicate: Cell<(E) -> Boolean>,
 ) : AbstractFilteredListCell<E>(list) {
diff --git a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/SimpleListCell.kt b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/SimpleListCell.kt
index d3abb449..74c8e3e0 100644
--- a/cell/src/commonMain/kotlin/world/phantasmal/cell/list/SimpleListCell.kt
+++ b/cell/src/commonMain/kotlin/world/phantasmal/cell/list/SimpleListCell.kt
@@ -6,7 +6,7 @@ import world.phantasmal.core.unsafe.unsafeCast
 /**
  * @param elements The backing list for this [ListCell].
  */
-class SimpleListCell<E>(
+internal class SimpleListCell<E>(
     private var elements: MutableList<E>,
 ) : AbstractListCell<E>(), MutableListCell<E> {
 
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/DelegatingCellTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/DelegatingCellTests.kt
index 38282cb5..d114d667 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/DelegatingCellTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/DelegatingCellTests.kt
@@ -14,7 +14,7 @@ class DelegatingCellTests : RegularCellTests, MutableCellTests<Int> {
         override fun createValue(): Int = v + 1
     }
 
-    override fun <T> createWithValue(value: T): DelegatingCell<T> {
+    override fun <T> createWithValue(value: T): Cell<T> {
         var v = value
         return DelegatingCell({ v }, { v = it })
     }
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/DependentCellTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/DependentCellTests.kt
index 2ed84412..5320633d 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/DependentCellTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/DependentCellTests.kt
@@ -4,7 +4,7 @@ package world.phantasmal.cell
 class DependentCellTests : RegularCellTests, CellWithDependenciesTests {
     override fun createProvider() = Provider()
 
-    override fun <T> createWithValue(value: T): DependentCell<T> {
+    override fun <T> createWithValue(value: T): Cell<T> {
         val dependency = SimpleCell(value)
         return DependentCell(dependency) { dependency.value }
     }
@@ -13,7 +13,7 @@ class DependentCellTests : RegularCellTests, CellWithDependenciesTests {
         dependency1: Cell<Int>,
         dependency2: Cell<Int>,
         dependency3: Cell<Int>,
-    ) =
+    ): Cell<Any> =
         DependentCell(dependency1, dependency2, dependency3) {
             dependency1.value + dependency2.value + dependency3.value
         }
@@ -21,7 +21,7 @@ class DependentCellTests : RegularCellTests, CellWithDependenciesTests {
     class Provider : CellTests.Provider {
         private val dependencyCell = SimpleCell(1)
 
-        override val cell = DependentCell(dependencyCell) { 2 * dependencyCell.value }
+        override val cell: Cell<Any> = DependentCell(dependencyCell) { 2 * dependencyCell.value }
 
         override fun emit() {
             dependencyCell.value += 2
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/DependentCellWithSimpleListCellTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/DependentCellWithSimpleListCellTests.kt
index 91edf65f..61a68110 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/DependentCellWithSimpleListCellTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/DependentCellWithSimpleListCellTests.kt
@@ -9,7 +9,7 @@ class DependentCellWithSimpleListCellTests : CellTests {
     class Provider : CellTests.Provider {
         private val dependencyCell = SimpleListCell(mutableListOf("a", "b", "c"))
 
-        override val cell = DependentCell(dependencyCell) { dependencyCell.value }
+        override val cell: Cell<Any> = DependentCell(dependencyCell) { dependencyCell.value }
 
         override fun emit() {
             dependencyCell.add("x")
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/FlatteningDependentCellDirectAndTransitiveDependencyEmitTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/FlatteningDependentCellDirectAndTransitiveDependencyEmitTests.kt
index 3471df39..650f6ab1 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/FlatteningDependentCellDirectAndTransitiveDependencyEmitTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/FlatteningDependentCellDirectAndTransitiveDependencyEmitTests.kt
@@ -12,7 +12,7 @@ class FlatteningDependentCellDirectAndTransitiveDependencyEmitTests : CellTests
         // This cell is both the direct and transitive dependency.
         private val dependencyCell = SimpleCell('a')
 
-        override val cell = FlatteningDependentCell(dependencyCell) { dependencyCell }
+        override val cell: Cell<Any> = FlatteningDependentCell(dependencyCell) { dependencyCell }
 
         override fun emit() {
             dependencyCell.value += 1
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/FlatteningDependentCellDirectDependencyEmitsTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/FlatteningDependentCellDirectDependencyEmitsTests.kt
index c96e9a1a..7381e932 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/FlatteningDependentCellDirectDependencyEmitsTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/FlatteningDependentCellDirectDependencyEmitsTests.kt
@@ -22,7 +22,7 @@ class FlatteningDependentCellDirectDependencyEmitsTests : RegularCellTests {
         }
     }
 
-    override fun <T> createWithValue(value: T): FlatteningDependentCell<T> {
+    override fun <T> createWithValue(value: T): Cell<T> {
         val v = ImmutableCell(ImmutableCell(value))
         return FlatteningDependentCell(v) { v.value }
     }
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/FlatteningDependentCellTransitiveDependencyEmitsTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/FlatteningDependentCellTransitiveDependencyEmitsTests.kt
index bb24af27..a1052bbe 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/FlatteningDependentCellTransitiveDependencyEmitsTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/FlatteningDependentCellTransitiveDependencyEmitsTests.kt
@@ -10,7 +10,7 @@ class FlatteningDependentCellTransitiveDependencyEmitsTests :
 
     override fun createProvider() = Provider()
 
-    override fun <T> createWithValue(value: T): FlatteningDependentCell<T> {
+    override fun <T> createWithValue(value: T): Cell<T> {
         val dependency = ImmutableCell(ImmutableCell(value))
         return FlatteningDependentCell(dependency) { dependency.value }
     }
@@ -19,7 +19,7 @@ class FlatteningDependentCellTransitiveDependencyEmitsTests :
         dependency1: Cell<Int>,
         dependency2: Cell<Int>,
         dependency3: Cell<Int>,
-    ) =
+    ): Cell<Any> =
         FlatteningDependentCell(dependency1, dependency2, dependency3) {
             ImmutableCell(dependency1.value + dependency2.value + dependency3.value)
         }
@@ -31,7 +31,7 @@ class FlatteningDependentCellTransitiveDependencyEmitsTests :
         // The direct dependency of the cell under test can't change.
         private val directDependency = ImmutableCell(transitiveDependency)
 
-        override val cell =
+        override val cell: Cell<Any> =
             FlatteningDependentCell(directDependency) { directDependency.value }
 
         override fun emit() {
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/SimpleCellTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/SimpleCellTests.kt
index 06f9f154..f65e8d6a 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/SimpleCellTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/SimpleCellTests.kt
@@ -12,5 +12,5 @@ class SimpleCellTests : RegularCellTests, MutableCellTests<Int> {
         override fun createValue(): Int = cell.value + 1
     }
 
-    override fun <T> createWithValue(value: T) = SimpleCell(value)
+    override fun <T> createWithValue(value: T): Cell<T> = SimpleCell(value)
 }
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/DependentListCellTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/DependentListCellTests.kt
index 7aece41e..326e7d4e 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/DependentListCellTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/DependentListCellTests.kt
@@ -13,7 +13,7 @@ class DependentListCellTests : ListCellTests, CellWithDependenciesTests {
         dependency1: Cell<Int>,
         dependency2: Cell<Int>,
         dependency3: Cell<Int>,
-    ) =
+    ): Cell<Any> =
         DependentListCell(dependency1, dependency2, dependency3) {
             listOf(dependency1.value, dependency2.value, dependency3.value)
         }
@@ -22,7 +22,7 @@ class DependentListCellTests : ListCellTests, CellWithDependenciesTests {
         private val dependencyCell =
             SimpleListCell(if (empty) mutableListOf() else mutableListOf(5))
 
-        override val cell =
+        override val cell: ListCell<Any> =
             DependentListCell(dependencyCell) { dependencyCell.value.map { 2 * it } }
 
         override fun addElement() {
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellListDependencyEmitsTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellListDependencyEmitsTests.kt
index 22884ecc..b4957f2c 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellListDependencyEmitsTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellListDependencyEmitsTests.kt
@@ -31,7 +31,7 @@ class FilteredListCellListDependencyEmitsTests : ListCellTests, CellWithDependen
         dependency1: Cell<Int>,
         dependency2: Cell<Int>,
         dependency3: Cell<Int>,
-    ) =
+    ): Cell<Any> =
         FilteredListCell(
             list = dependency1.mapToList { listOf(it) },
             predicate = dependency2.map { value2 ->
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellPredicateDependencyEmitsTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellPredicateDependencyEmitsTests.kt
index c93f88a2..baade308 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellPredicateDependencyEmitsTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellPredicateDependencyEmitsTests.kt
@@ -9,6 +9,7 @@ import world.phantasmal.cell.*
 class FilteredListCellPredicateDependencyEmitsTests : ListCellTests, CellWithDependenciesTests {
     override fun createListProvider(empty: Boolean) = object : ListCellTests.Provider {
         private var maxValue = if (empty) 0 else 1
+
         // The predicate cell changes, the predicate results don't.
         private val predicateCell = SimpleCell<(Int) -> Cell<Boolean>> { cell(it <= maxValue) }
 
@@ -30,7 +31,7 @@ class FilteredListCellPredicateDependencyEmitsTests : ListCellTests, CellWithDep
         dependency1: Cell<Int>,
         dependency2: Cell<Int>,
         dependency3: Cell<Int>,
-    ) =
+    ): Cell<Any> =
         FilteredListCell(
             list = listCell(1, 2, 3, 4, 5, 6, 7, 8, 9),
             predicate = map(dependency1, dependency2, dependency3) { value1, value2, value3 ->
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellPredicateResultDependenciesEmitTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellPredicateResultDependenciesEmitTests.kt
index 083afdde..4e0a3139 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellPredicateResultDependenciesEmitTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellPredicateResultDependenciesEmitTests.kt
@@ -31,7 +31,7 @@ class FilteredListCellPredicateResultDependenciesEmitTests : ListCellTests,
         dependency1: Cell<Int>,
         dependency2: Cell<Int>,
         dependency3: Cell<Int>,
-    ): FilteredListCell<Int> {
+    ): Cell<Any> {
         val deps = listOf(dependency1, dependency2, dependency3)
 
         return FilteredListCell(
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellTests.kt
index e665d708..74fd2bc1 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FilteredListCellTests.kt
@@ -12,6 +12,9 @@ import world.phantasmal.cell.map
  */
 @Suppress("unused")
 class FilteredListCellTests : AbstractFilteredListCellTests {
-    override fun <E> createFilteredListCell(list: ListCell<E>, predicate: Cell<(E) -> Boolean>) =
+    override fun <E> createFilteredListCell(
+        list: ListCell<E>,
+        predicate: Cell<(E) -> Boolean>,
+    ): ListCell<E> =
         FilteredListCell(list, predicate.map { p -> { cell(p(it)) } })
 }
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FlatteningDependentListCellTransitiveDependencyEmitsTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FlatteningDependentListCellTransitiveDependencyEmitsTests.kt
index ccf508c7..28fcea74 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FlatteningDependentListCellTransitiveDependencyEmitsTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/FlatteningDependentListCellTransitiveDependencyEmitsTests.kt
@@ -21,7 +21,7 @@ class FlatteningDependentListCellTransitiveDependencyEmitsTests :
         dependency1: Cell<Int>,
         dependency2: Cell<Int>,
         dependency3: Cell<Int>,
-    ) =
+    ): Cell<Any> =
         FlatteningDependentListCell(dependency1, dependency2, dependency3) {
             ImmutableListCell(listOf(dependency1.value, dependency2.value, dependency3.value))
         }
@@ -34,7 +34,7 @@ class FlatteningDependentListCellTransitiveDependencyEmitsTests :
         // The direct dependency of the list under test can't change.
         private val directDependency = ImmutableCell<ListCell<Int>>(transitiveDependency)
 
-        override val cell =
+        override val cell: ListCell<Any> =
             FlatteningDependentListCell(directDependency) { directDependency.value }
 
         override fun addElement() {
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/ListElementsDependentCellElementEmitsTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/ListElementsDependentCellElementEmitsTests.kt
index f9acf8d3..02614e16 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/ListElementsDependentCellElementEmitsTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/ListElementsDependentCellElementEmitsTests.kt
@@ -1,11 +1,6 @@
 package world.phantasmal.cell.list
 
-import world.phantasmal.cell.Cell
-import world.phantasmal.cell.CellTests
-import world.phantasmal.cell.CellWithDependenciesTests
-import world.phantasmal.cell.DependentCell
-import world.phantasmal.cell.MutableCell
-import world.phantasmal.cell.SimpleCell
+import world.phantasmal.cell.*
 
 /**
  * In these tests, the direct list cell dependency of the [ListElementsDependentCell] doesn't
@@ -33,7 +28,7 @@ class ListElementsDependentCellElementEmitsTests : CellWithDependenciesTests {
         dependency1: Cell<Int>,
         dependency2: Cell<Int>,
         dependency3: Cell<Int>,
-    ) =
+    ): Cell<Any> =
         ListElementsDependentCell(
             ImmutableListCell(listOf(dependency1, dependency2, dependency3))
         ) { arrayOf(it) }
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/SimpleFilteredListCellListDependencyEmitsTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/SimpleFilteredListCellListDependencyEmitsTests.kt
index 43fd8c3c..57618471 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/SimpleFilteredListCellListDependencyEmitsTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/SimpleFilteredListCellListDependencyEmitsTests.kt
@@ -30,7 +30,7 @@ class SimpleFilteredListCellListDependencyEmitsTests :
         dependency1: Cell<Int>,
         dependency2: Cell<Int>,
         dependency3: Cell<Int>,
-    ) =
+    ): Cell<Any> =
         SimpleFilteredListCell(
             list = mapToList(dependency1, dependency2, dependency3) { value1, value2, value3 ->
                 listOf(value1, value2, value3)
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/SimpleFilteredListCellPredicateDependencyEmitsTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/SimpleFilteredListCellPredicateDependencyEmitsTests.kt
index a30b0e42..5de6a28d 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/SimpleFilteredListCellPredicateDependencyEmitsTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/SimpleFilteredListCellPredicateDependencyEmitsTests.kt
@@ -33,7 +33,7 @@ class SimpleFilteredListCellPredicateDependencyEmitsTests :
         dependency1: Cell<Int>,
         dependency2: Cell<Int>,
         dependency3: Cell<Int>,
-    ) =
+    ): Cell<Any> =
         SimpleFilteredListCell(
             list = listCell(1, 2, 3, 4, 5, 6, 7, 8, 9),
             predicate = map(dependency1, dependency2, dependency3) { value1, value2, value3 ->
diff --git a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/SimpleFilteredListCellTests.kt b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/SimpleFilteredListCellTests.kt
index 043d5e5c..13cdb455 100644
--- a/cell/src/commonTest/kotlin/world/phantasmal/cell/list/SimpleFilteredListCellTests.kt
+++ b/cell/src/commonTest/kotlin/world/phantasmal/cell/list/SimpleFilteredListCellTests.kt
@@ -10,6 +10,9 @@ import world.phantasmal.cell.Cell
  */
 @Suppress("unused")
 class SimpleFilteredListCellTests : AbstractFilteredListCellTests {
-    override fun <E> createFilteredListCell(list: ListCell<E>, predicate: Cell<(E) -> Boolean>) =
+    override fun <E> createFilteredListCell(
+        list: ListCell<E>,
+        predicate: Cell<(E) -> Boolean>,
+    ): ListCell<E> =
         SimpleFilteredListCell(list, predicate)
 }
diff --git a/web/src/main/kotlin/world/phantasmal/web/questEditor/models/QuestEventModel.kt b/web/src/main/kotlin/world/phantasmal/web/questEditor/models/QuestEventModel.kt
index a4638843..d3a22dca 100644
--- a/web/src/main/kotlin/world/phantasmal/web/questEditor/models/QuestEventModel.kt
+++ b/web/src/main/kotlin/world/phantasmal/web/questEditor/models/QuestEventModel.kt
@@ -2,7 +2,7 @@ package world.phantasmal.web.questEditor.models
 
 import world.phantasmal.cell.Cell
 import world.phantasmal.cell.list.ListCell
-import world.phantasmal.cell.list.SimpleListCell
+import world.phantasmal.cell.list.mutableListCell
 import world.phantasmal.cell.map
 import world.phantasmal.cell.mutableCell
 
@@ -19,7 +19,7 @@ class QuestEventModel(
     private val _sectionId = mutableCell(sectionId)
     private val _waveId = mutableCell(waveId)
     private val _delay = mutableCell(delay)
-    private val _actions = SimpleListCell(actions)
+    private val _actions = mutableListCell(actions)
 
     val id: Cell<Int> = _id
     val sectionId: Cell<Int> = _sectionId
diff --git a/web/src/main/kotlin/world/phantasmal/web/questEditor/models/QuestModel.kt b/web/src/main/kotlin/world/phantasmal/web/questEditor/models/QuestModel.kt
index 41ce9b9e..e82e0da3 100644
--- a/web/src/main/kotlin/world/phantasmal/web/questEditor/models/QuestModel.kt
+++ b/web/src/main/kotlin/world/phantasmal/web/questEditor/models/QuestModel.kt
@@ -1,15 +1,15 @@
 package world.phantasmal.web.questEditor.models
 
+import world.phantasmal.cell.Cell
+import world.phantasmal.cell.list.ListCell
+import world.phantasmal.cell.list.flatMapToList
+import world.phantasmal.cell.list.listCell
+import world.phantasmal.cell.list.mutableListCell
+import world.phantasmal.cell.map
+import world.phantasmal.cell.mutableCell
 import world.phantasmal.psolib.Episode
 import world.phantasmal.psolib.asm.BytecodeIr
 import world.phantasmal.psolib.fileFormats.quest.DatUnknown
-import world.phantasmal.cell.Cell
-import world.phantasmal.cell.list.ListCell
-import world.phantasmal.cell.list.SimpleListCell
-import world.phantasmal.cell.list.flatMapToList
-import world.phantasmal.cell.list.listCell
-import world.phantasmal.cell.map
-import world.phantasmal.cell.mutableCell
 
 class QuestModel(
     id: Int,
@@ -36,9 +36,9 @@ class QuestModel(
     private val _shortDescription = mutableCell("")
     private val _longDescription = mutableCell("")
     private val _mapDesignations = mutableCell(mapDesignations)
-    private val _npcs = SimpleListCell(npcs)
-    private val _objects = SimpleListCell(objects)
-    private val _events = SimpleListCell(events)
+    private val _npcs = mutableListCell(npcs)
+    private val _objects = mutableListCell(objects)
+    private val _events = mutableListCell(events)
 
     val id: Cell<Int> = _id
     val language: Cell<Int> = _language
diff --git a/webui/src/main/kotlin/world/phantasmal/webui/LoadingStatusCell.kt b/webui/src/main/kotlin/world/phantasmal/webui/LoadingStatusCell.kt
index 3b75a4be..9d4c5eed 100644
--- a/webui/src/main/kotlin/world/phantasmal/webui/LoadingStatusCell.kt
+++ b/webui/src/main/kotlin/world/phantasmal/webui/LoadingStatusCell.kt
@@ -3,7 +3,8 @@ package world.phantasmal.webui
 import kotlinx.coroutines.*
 import mu.KotlinLogging
 import world.phantasmal.cell.Cell
-import world.phantasmal.cell.SimpleCell
+import world.phantasmal.cell.MutableCell
+import world.phantasmal.cell.mutableCell
 import kotlin.time.measureTime
 
 private val logger = KotlinLogging.logger {}
@@ -26,14 +27,14 @@ class LoadingStatusCellImpl private constructor(
     private val dataName: String,
     /** Will be called with [Dispatchers.Main] context. */
     private val loadData: suspend () -> Unit,
-    private val cellDelegate: SimpleCell<LoadingStatus>,
+    private val cellDelegate: MutableCell<LoadingStatus>,
 ) : LoadingStatusCell, Cell<LoadingStatus> by cellDelegate {
 
     constructor(
         scope: CoroutineScope,
         dataName: String,
         loadData: suspend () -> Unit,
-    ) : this(scope, dataName, loadData, SimpleCell(LoadingStatus.Uninitialized))
+    ) : this(scope, dataName, loadData, mutableCell(LoadingStatus.Uninitialized))
 
     private var currentJob: Job? = null