diff --git a/src/field/arena.ts b/src/field/arena.ts
index b3a455c865b..4f243789567 100644
--- a/src/field/arena.ts
+++ b/src/field/arena.ts
@@ -312,7 +312,7 @@ export class Arena {
   /**
    * Attempts to set a new weather to the battle
    * @param weather {@linkcode WeatherType} new {@linkcode WeatherType} to set
-   * @param hasPokemonSource boolean if the new weather is from a pokemon
+   * @param user {@linkcode Pokemon} that caused the weather effect
    * @returns true if new weather set, false if no weather provided or attempting to set the same weather as currently in use
    */
   trySetWeather(weather: WeatherType, user?: Pokemon): boolean {
@@ -406,6 +406,13 @@ export class Arena {
     return !(this.terrain?.terrainType === (terrain || undefined));
   }
 
+  /**
+   * Attempts to set a new terrain effect to the battle
+   * @param terrain {@linkcode TerrainType} new {@linkcode TerrainType} to set
+   * @param ignoreAnim boolean if the terrain animation should be ignored
+   * @param user {@linkcode Pokemon} that caused the terrain effect
+   * @returns true if new terrain set, false if no terrain provided or attempting to set the same terrain as currently in use
+   */
   trySetTerrain(terrain: TerrainType, ignoreAnim = false, user?: Pokemon): boolean {
     if (!this.canSetTerrain(terrain)) {
       return false;
diff --git a/src/modifier/modifier.ts b/src/modifier/modifier.ts
index e5c790ef512..7c9207bbea5 100644
--- a/src/modifier/modifier.ts
+++ b/src/modifier/modifier.ts
@@ -2014,7 +2014,20 @@ export class ResetNegativeStatStageModifier extends PokemonHeldItemModifier {
   }
 }
 
+/**
+ * Modifier used for held items, namely Mystical Rock, that extend the
+ * duration of weather and terrain effects.
+ * @extends PokemonHeldItemModifier
+ * @see {@linkcode apply}
+ */
 export class FieldEffectModifier extends PokemonHeldItemModifier {
+  /**
+   * Provides two more turns per stack to any weather or terrain effect caused
+   * by the holder.
+   * @param pokemon {@linkcode Pokemon} that holds the held item
+   * @param fieldDuration {@linkcode NumberHolder} that stores the current field effect duration
+   * @returns `true` if the field effect extension was applied successfully
+   */
   override apply(_pokemon: Pokemon, fieldDuration: NumberHolder): boolean {
     fieldDuration.value += 2 * this.stackCount;
     return true;