Reflect works pretty great in the Yunalesca fight. Protects your Zombies from Cura/Curaga/Regen (although you better dispel Yunalesca's Regen) and I think it also bounces back the status effect spell counters in the first phase.

Ah yes, Dark Bahamut, one of the three Dark Aeons that really trolls American FFX HD players. Admittedly his placement right on top of the Sun Crest is pretty thoughtless. One of the most fun superboss battles in the game, though.