diff --git a/src/data/pokemon-evolutions.ts b/src/data/pokemon-evolutions.ts
index 696cf006ad0..236d174492f 100644
--- a/src/data/pokemon-evolutions.ts
+++ b/src/data/pokemon-evolutions.ts
@@ -1145,6 +1145,11 @@ export const pokemonEvolutions: PokemonEvolutions = {
     new SpeciesEvolution(Species.PAWMOT, 32, null, null)
   ],
   [Species.TANDEMAUS]: [
+    new SpeciesFormEvolution(Species.MAUSHOLD, "", "three", 25, null, new SpeciesEvolutionCondition(p => {
+      let ret = false;
+      p.scene.executeWithSeedOffset(() => ret = !Utils.randSeedInt(4), p.id);
+      return ret;
+    })),
     new SpeciesEvolution(Species.MAUSHOLD, 25, null, null)
   ],
   [Species.FIDOUGH]: [
diff --git a/src/data/pokemon-species.ts b/src/data/pokemon-species.ts
index 77134cca190..eb2ad358c65 100644
--- a/src/data/pokemon-species.ts
+++ b/src/data/pokemon-species.ts
@@ -2459,8 +2459,8 @@ export function initSpecies() {
     new PokemonSpecies(Species.PAWMOT, 9, false, false, false, "Hands-On Pokémon", Type.ELECTRIC, Type.FIGHTING, 0.9, 41, Abilities.VOLT_ABSORB, Abilities.NATURAL_CURE, Abilities.IRON_FIST, 490, 70, 115, 70, 70, 60, 105, 45, 50, 245, GrowthRate.MEDIUM_FAST, 50, false),
     new PokemonSpecies(Species.TANDEMAUS, 9, false, false, false, "Couple Pokémon", Type.NORMAL, null, 0.3, 1.8, Abilities.RUN_AWAY, Abilities.PICKUP, Abilities.OWN_TEMPO, 305, 50, 50, 45, 40, 45, 75, 150, 50, 61, GrowthRate.FAST, null, false),
     new PokemonSpecies(Species.MAUSHOLD, 9, false, false, false, "Family Pokémon", Type.NORMAL, null, 0.3, 2.3, Abilities.FRIEND_GUARD, Abilities.CHEEK_POUCH, Abilities.TECHNICIAN, 470, 74, 75, 70, 65, 75, 111, 75, 50, 165, GrowthRate.FAST, null, false, false,
-      new PokemonForm("Family of Four", "four", Type.NORMAL, null, 0.3, 2.3, Abilities.FRIEND_GUARD, Abilities.CHEEK_POUCH, Abilities.TECHNICIAN, 470, 74, 75, 70, 65, 75, 111, 75, 50, 165),
-      new PokemonForm("Family of Three", "three", Type.NORMAL, null, 0.3, 2.8, Abilities.FRIEND_GUARD, Abilities.CHEEK_POUCH, Abilities.TECHNICIAN, 470, 74, 75, 70, 65, 75, 111, 75, 50, 165),
+      new PokemonForm("Family of Four", "four", Type.NORMAL, null, 0.3, 2.8, Abilities.FRIEND_GUARD, Abilities.CHEEK_POUCH, Abilities.TECHNICIAN, 470, 74, 75, 70, 65, 75, 111, 75, 50, 165),
+      new PokemonForm("Family of Three", "three", Type.NORMAL, null, 0.3, 2.3, Abilities.FRIEND_GUARD, Abilities.CHEEK_POUCH, Abilities.TECHNICIAN, 470, 74, 75, 70, 65, 75, 111, 75, 50, 165),
     ),
     new PokemonSpecies(Species.FIDOUGH, 9, false, false, false, "Puppy Pokémon", Type.FAIRY, null, 0.3, 10.9, Abilities.OWN_TEMPO, Abilities.NONE, Abilities.KLUTZ, 312, 37, 55, 70, 30, 55, 65, 190, 50, 62, GrowthRate.MEDIUM_SLOW, 50, false),
     new PokemonSpecies(Species.DACHSBUN, 9, false, false, false, "Dog Pokémon", Type.FAIRY, null, 0.5, 14.9, Abilities.WELL_BAKED_BODY, Abilities.NONE, Abilities.AROMA_VEIL, 477, 57, 80, 115, 50, 80, 95, 90, 50, 167, GrowthRate.MEDIUM_SLOW, 50, false),
diff --git a/src/test/evolutions/evolutions.test.ts b/src/test/evolutions/evolutions.test.ts
new file mode 100644
index 00000000000..4e38e72bb7c
--- /dev/null
+++ b/src/test/evolutions/evolutions.test.ts
@@ -0,0 +1,48 @@
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
+import Phaser from "phaser";
+import GameManager from "#app/test/utils/gameManager";
+import { Species } from "#enums/species";
+import * as Utils from "#app/utils";
+
+describe("Evolution tests", () => {
+  let phaserGame: Phaser.Game;
+  let game: GameManager;
+
+  beforeAll(() => {
+    phaserGame = new Phaser.Game({
+      type: Phaser.HEADLESS,
+    });
+  });
+
+  afterEach(() => {
+    game.phaseInterceptor.restoreOg();
+  });
+
+  beforeEach(() => {
+    game = new GameManager(phaserGame);
+  });
+
+  it("tandemaus evolution form test", async () => {
+    /* this test checks to make sure that tandemaus will
+     * evolve into a 3 family maushold 25% of the time
+     * and a 4 family maushold the other 75% of the time
+     * This is done by using the getEvolution method in pokemon.ts
+     * getEvolution will give back the form that the pokemon can evolve into
+     * It does this by checking the pokemon conditions in pokemon-forms.ts
+     * For tandemaus, the conditions are random due to a randSeedInt(4)
+     * If the value is 0, it's a 3 family maushold, whereas if the value is
+     * 1, 2 or 3, it's a 4 family maushold
+     */
+    await game.startBattle([Species.TANDEMAUS]); // starts us off with a tandemaus
+    const playerPokemon = game.scene.getPlayerPokemon();
+    playerPokemon.level = 25; // tandemaus evolves at level 25
+    vi.spyOn(Utils, "randSeedInt").mockReturnValue(0); // setting the random generator to be 0 to force a three family maushold
+    const threeForm = playerPokemon.getEvolution();
+    expect(threeForm.evoFormKey).toBe("three"); // as per pokemon-forms, the evoFormKey for 3 family mausholds is "three"
+    for (let f = 1; f < 4; f++) {
+      vi.spyOn(Utils, "randSeedInt").mockReturnValue(f); // setting the random generator to 1, 2 and 3 to force 4 family mausholds
+      const fourForm = playerPokemon.getEvolution();
+      expect(fourForm.evoFormKey).toBe(null); // meanwhile, according to the pokemon-forms, the evoFormKey for a 4 family maushold is null
+    }
+  }, 5000);
+});