While there are plenty of large and powerful new Pokémon in Pokémon Scarlet and Violet, a fast fan favorite is Tandemaus, a Pokémon comprised of two separate mouse-like rodent Pokémon that work together as one. They are absolutely adorable.
To make things even cuter, Tandemaus' evolution Maushold consists of those original dual mice but now with two baby mice as well. While the larger mice are certainly a bit protective, trainers are discovering that the lovely little mouse family is still very capable on the battlefield.
There are a lot of strange rumors about how and when Tandemaus evolves, so we've got the confirmed evolution details for you right here.
How to evolve Tandemaus into Maushold
While there are some reported cases of Tandemaus evolving randomly in a box or while exploring Paldeaa, we didn't run into that in our testing. Evolving Tandemaus into Maushold is really simple, but there's a specific way to do so if you want to see the evolution animation.
Tandemaus can evolve into Maushold starting at level 25 only when leveled up in a battle. You cannot use XP or Rare Candies to evolve Tandemaus — it will simply level up without evolving.
If you cause an opposing Pokémon to faint in battle using Tandemaus, you will get the standard evolution animation post-battle. But if Tandemaus levels up through experience share (say you use another Pokémon to win a trainer battle), it will evolve off-screen. Just look in your party in an should be a Maushold.
Maushold alternative forms
Maushold will typically consist of four mice Pokémon (two parents and two children), but there is a rare form that switches things up a bit.
Maushold also has a form that only has one youngling. According to Bulbagarden, the evolution form is determined by its encryption constant, with a 1/100 chance of Tandemaus evolving into a family of three Maushold. These odds are different for Mausholds found in Tera Raid Battles.