Barrier Tower, a one time dungeon filled with nasty encounter. There is no way to restock once you launch the attack. While the enemies are nasty, none of them has resistance to Petrify. So Break Spellblade and watch as anything fall in a single hit. The only exception to that is the Yellow Dragons. Whereas most enemies still has 1000 HP, Yellow Dragon has 8500. Their single target and multi target attack also hurts a freaking lot. And you fight 2 of them at once. Have fun! Wish I had access to Death. Also, I hate Reflect Knight. They're tough, hits hard, and reflect your magic (Break Spellblade then).
Anyway, the third and possibly final boss that's on my crap list is Atomos, a freaky abomination of time with a big mouth that is used to eat any fallen character and send then to void.
On top of having loads of HP and no weakness, it uses Comet twice as its primary attack. Comet deals random damage and may deals 1000+ damage. So I have to get lucky and hope it won't hit the same character twice or deals more than 1000 damage. If there's a KO'ed character in the field, then it will gradually suck them toward it's mouth to Banish them. On top of Comet, it also has Slowga and Old. Both of which I can't remedy easily since I don't have Hastega and I can't use Esuna. That bastard also immune to Slow and in a state of permanent Haste.
I think it's weak to Sleep? I don't know, I try it multiple times and I can't seem to inflict it. Maiden Kiss + Turtle Shell deals great damage to it, I have Blue Magic for level and defense debuff, and Comet can deal 1000 damage against that douche as well. Phoenix Down + Ether (Resurrection) may help, but not by much. Wish I have Level 5 Death since Dark Arts + Level 5 Death = short battle.