Snails as a morph. They are slower, but they aren't hurt by spikes (Bonus points if you know why) and they can stick to walls. Also, They only have so much slime. Collecting a bolt restores 5% slime. When they run out of slime, they are immobile.
Fun game, but upgrading could be better. I would rather pick my own upgrade and have the next level "adapt" rather then pre-made choices. Also, can you really call this a bullet hell, it was pretty easy in my opinion.