Penguins are enemies found in Wario Land II, where they are members of the Black Sugar Gang. They look like bipedal penguins with a menacing beak and a bandanna tied around their head. In the English version of the game, they carry large black orbs with them, which they will throw at Wario if he gets in range. If the orb hits Wario, he will become dizzy and controlling him will become much harder. Penguins mostly appear in areas with small platforms and many opportunities to fall down a pit. There is also always a body of water near them which can be used to cure the status ailments they evoke.
In the Japanese version of Wario Land II, Penguins carry around beer mugs instead of iron orbs. When they notice Wario, they intoxicate him by splashing alcohol on his face. The beer mugs were most likely removed to censor any reference to alcohol consumption.
Names in other languages