The presentation is great, and the music is super catchy! I like the main mechanic as well. I think the switching back and forth could be a bit clearer, since it happens when you kill an enemy or when you take damage--sometimes I'm unsure of which has happened. And it's not always clear if I'm taking damage from an enemy or from shooting myself. This is a super cool concept, though, and I could see that mechanic being expanded upon! What if possessing different types of enemies gave the player different abilities?