This is really clever! I love games like these, it's a tense experience. The challenge builds very appropriately, although by the last two or three levels I had developed an easy strategy that was pretty much fool-proof. I like the background art too, even though I'd love to see more of it. With some more time I imagine this could be a really long-lasting game, with some fitting music, more environments, and possibly some feature implemented that makes it so the characters don't overlap as often, as I found that to be the main difficulty when tagging them. Maybe there could be some twists to some of the levels, so you have to switch up your strategy?