I'm playing through FFX right now, and I gotta say, Lady Yunalesca is downright frustrating.

For one, she cast Zombie on you, and then heals you. That in turn damages you instead of heals you. You then cannot heal YOURSELF, or cure yourself, because she also cast curse, which makes Esuna and Holy Water actually miss and you cannot cure it except for killing yourself and then using a phoenix down, but then she just does it all over again. I am racking my head against the wall trying to kill this boss.

What are the most frustrating boss battles you've fought?