Gabes Game
There have been countless platformers made. In many of those, there are a wide variety of enemies. So if you couldn't count the number of platformers made, you really can't count the number of side scrolling enemies in existence. So while you're not counting, how do you find originality?
You don't. You find what makes your specific game fun, then you push the player to experience that. I've found that the coolest moments in my game, are when I'm doing sweet air combos. Jumping from one enemy to another, or sending one enemy flying into his buddy. Essentially, the game is most fun when the player isn't touching the ground.