Hm.... I don't exactly remember, but I think it was a flying imp thing in Legasista. Stupid Demon and Hell gates leveling up the monsters in the place. Lucky me, my generated floor happened to be a floor of a bunch of imps in a very, veeeeeery thin corridor with a bunch of giant mushrooms blocking paths and the imps towering my character's levels by a good 15 levels or so. Needless to say, once I got cornered, it was over.