O.K. so a "kill tile" is an actor that looks like a tile so that you can attack it. I am pretty sure you could use an actual tile and kill that just make it differ slightly from your actual tile. I saw a post where you can click a tile and it deletes it, berhaps you could do the same but instead of clicking, it would have to colide with your character while in the punch animation?
But I don't know much stencyl, so this is just an idea, I am trying to help out a bit, because helping you helps me.
Hope it helped? :S
Skye