Gem (Wario: Master of Disguise)
From the Super Mario Wiki
Gems are collectibles found in Wario: Master of Disguise. They can be found by defeating enemies or shooting Sapphire Stars. When Wario picks one up, Goodstyle eats it, causing one of Wario's disguises to gain experience. There are eight different types of gems, each corresponding to one of Wario's disguises, all of which come in two sizes: small and large. After Wario collects enough gems of a specific type, one of his disguises will level up, causing him to deal more damage while wearing that disguise. Each disguise begins at level 1 and maxes out as level 3.
This is the list of gems in the game and which form they power up: