Cucco from 'The Legend of Zelda' series immediately comes to mind. These seemingly harmless chickens turn into terrifying forces of nature when provoked, swarming the player in a hilarious yet deadly fashion.
What makes them iconic isn't just their retaliation mechanic, but how they subvert expectations in a fantasy adventure game. The series has conditioned players to view them as background elements until that first unforgettable attack. Their high-pitched alarm calls have become a cultural touchstone, inspiring countless memes about their unexpected power.