Disclaimer: This isn't really a serious suggestion.

I noticed that there are different colored energy knight things (the ones that shock people/themselves). It would be cool if each kind of energy knight had it's own strength and weakness. And then you could set it up so that you'd have like 6 different energy knights. Then, whenever you get an energy knight powerup in a level, instead of summoning a generic energy knight, you get to summon an energy knight of your choosing from your energy knight belt.

That would be for PvE. But you could make a 1v1 PvP system where the players can't do damage to anyone, and instead try to win by summoning energy knights. The person who has all 6 of their energy knights faint would lose and the other person would win.