Mallow's Tsareena is the evolved form of
Mallow's Steenee. It evolved when it banged on the top of a cage that
Ash Ketchum was caught in and it learned the move Stomp as a result of its efforts.
It battled against
Lana's Primarina in the Top 16 round of the Alola League.
Mallow was going to give in as she didn't want Tsareena to keep fighting a losing battle. It didn't want to quit and it convinced her to keep on fighting and they performed the Z-Move Bloom Doom for the first time.
Lana's Primarina countered with the Oceanic Operetta Z-Move and they ended up cancelling each other out. Primarina ended up winning the match.