For me, surveyors and any sort of rat are both pretty bad, since they move around too much. The hardest part of the hyperion circle of slaughter is finding all the surveyors flying around above you when you're trying to focus on all the other baddies coming at you.
That reminds me of one of the least fair enemies actually. Hyperion Hawks and their other difficulty variant, soon to be variants. They look like the other Hyperion soldiers, but have those blasted jetpacks and what seems to be instant-hit instant-FFYL Rocket Launchers. Screw those guys. --- Spell card! Diamond Will ~ Unbreakable Determination!