Jeane in No More Heroes is indeed pretty savage as somebody already pointed out. Dire Miralis in MHTri U was a world of "lolnope."
The semi-final boss in FF Tactics A2, whose name i do not recall. She had this ability to full-heal herself which she could use at any point at no cost to her. Would've been easier if the devs had just replaced her with a giant hand flipping the bird leading to an automatic game over...
Monster Hunter: pissing me off since 2010.