The ant-pus-things in singularity bug (hoho) the hell out of me because they often appear in areas you can't predict at point blank range and then explode. You're supposed to be able to do little tactics to them that render them easy but the first indication I ever get that they have popped up again is when I lose half my health to them randomly. It's most, most irritating. They're certainly not a candidate for the most unfair, cheap enemies ever, but they're really really really annoying.