Got 2.
First is the Cameo Team from Tales of Symphonia, in Mania. I've hardly managed to get by in Hard, with Glory Presea, Zelos and Raine, yet, the Enemy using Life Bottles right after you've dealt with Meredy, who ironocally casts Indignation on you quite often, is the worst.
Second, the Sylph in Mania, from ToS too. They're definitely beatable, but Fairess continiously interrupting Raine's Revitalize makes this battle a torture without Concentrate and Glory. I've managed after several attempts, however.