diff --git a/src/battle-scene.ts b/src/battle-scene.ts
index 271cde1aaa9..52af0c1b706 100644
--- a/src/battle-scene.ts
+++ b/src/battle-scene.ts
@@ -1513,8 +1513,8 @@ export class BattleScene extends SceneBase {
     return this.currentBattle;
   }
 
-  newArena(biome: BiomeId, playerFaints?: number): Arena {
-    this.arena = new Arena(biome, BiomeId[biome].toLowerCase(), playerFaints);
+  newArena(biome: BiomeId, playerFaints = 0): Arena {
+    this.arena = new Arena(biome, playerFaints);
     this.eventTarget.dispatchEvent(new NewArenaEvent());
 
     this.arenaBg.pipelineData = {
diff --git a/src/field/arena.ts b/src/field/arena.ts
index 6f2310b95c2..2ce347b5337 100644
--- a/src/field/arena.ts
+++ b/src/field/arena.ts
@@ -54,7 +54,7 @@ export class Arena {
   public bgm: string;
   public ignoreAbilities: boolean;
   public ignoringEffectSource: BattlerIndex | null;
-  public playerTerasUsed: number;
+  public playerTerasUsed = 0;
   /**
    * Saves the number of times a party pokemon faints during a arena encounter.
    * {@linkcode globalScene.currentBattle.enemyFaints} is the corresponding faint counter for the enemy (this resets every wave).
@@ -68,12 +68,11 @@ export class Arena {
 
   public readonly eventTarget: EventTarget = new EventTarget();
 
-  constructor(biome: BiomeId, bgm: string, playerFaints = 0) {
+  constructor(biome: BiomeId, playerFaints = 0) {
     this.biomeType = biome;
-    this.bgm = bgm;
+    this.bgm = BiomeId[biome].toLowerCase();
     this.trainerPool = biomeTrainerPools[biome];
     this.updatePoolsForTimeOfDay();
-    this.playerTerasUsed = 0;
     this.playerFaints = playerFaints;
   }