Why isn’t my Tandemaus evolving?

Question

It’s well over level 25 yet it’s still not evolving when I level it up.

Comments

Are you leveling it up in a battle? Candies don't work.

---

You have to level it up in a battle?

---

remeber kids dont do drugs!

Answer 1

Tandemaus evolves into Maushold only when it's leveled up in a battle, so using Rare Candies or Exp. Candies won't work.

It's okay if it gains shared EXP by merely being present in your party, but if it didn't actually participate in the battle, it may evolve secretly without displaying the evolution screen.

Source: Experience + Tandemaus entries