WOW, this is easily one of the best games I've played so far!! The level of polish is off the charts, the pixel art graphics are excellently done, the movement and camera both feel really great, and it's a super creative idea the fits the theme extremely well. I love that that the game gives you more points for killing enemies using another enemy instead of pushing them into a pit to encourage you to use the more risky tactics.
However I couldn't help feeling like the game would be even better without the crystal. The game is at its best when you're using enemies to kill other enemies, but when the enemies keep targeting the crystal instead of the player, it's impossible to manipulate their AI. For example, I kept trying to bait the green enemies into shooting other enemies, but then I'd get frustrated when they just target the crystal instead of me. Maybe it would be more fun if the crystal just wasn't there, and enemies always target the player? This would let the player focus 100% on manipulating enemies into killing other enemies, without having to worry about them targeting the crystal instead.
Overall this is an excellent submission and I'm surprised it doesn't have more ratings!