Flora and Fauna
The old 'possessed animal or plant' foe. From the carnivorous plants of forgotten platform hero Dizzy (yes, he's an egg) to the psychotically aggressive dinosaurs of Turok, nature is an inexhaustible source of inspiration for games designers. Too lazy to invent a new enemy? Add in a plant that grabs players as they walk by. Or fish that jump out of water and bite you. Or birds that drop eggs on your head - that happens a lot in real life. Or how about a slavering dog? Better yet, make it a slavering zombie dog. Which leads us nicely onto our next foe...
Above: Turok, Kao Challengers, Fantastic Dizzy, Super Mario Bros, Resident Evil and Metroid Prime