Currently we have only two basic kinds of powerups; heal powerups in several grades, and the turret powerup.
I was thinking we could do "downgrades" too, since the enemy picks everything up. If we had a virus that enemies (or the player) would pick up and just commits self destruct, with an explosion! (which will affect a big radius).
This way the player wants to destroy the "bad" powerups, because if you pick it up you are game over (after self destruct) and if the enemy picks it up, and you are in a radius, you will get damage.