white mousse, marilith, orhtos, and lindwyrm

most of them i beat with this ridiculously basic tactic:

before running into battle i'd throw lure, haste, bravery, protect, and berserk on basch who's rocking a bubble belt that gives him something like 5000+ hp. i'd then hit the mark with dispel (if it's needed) and whatever status ailmements that will stick. in my experience, slow and blind have worked on most of them. the nipohlona or whatever the fuck it's called (it's the 30000 gil accessory available at the clan provisioner that reverses the effects of items) is extremely useful for hitting marks with status ailments. equip it and throw eye drops at the mark to make it blind, echo herbs to silence it, remedies... ;)

at this point, the mark is focused soley on bacsh who's hitting the mark for at least 1500 damage (depending on what weapon he's using) per hit, with each hit occuring around 3 times every 2 seconds (exlcuding combos). now the rest of your party is free to hang back and toss spells and heal as necessary. usually, fran and ashe hit themselves with haste & faith, hit the mark with shear, equip staves or rods, and sit back and throw shades of black (best tech in the game so far) at the mark. there's nothing better than watching basch hit a mark with a 7000+ damage 5-hit combo which is immediately followed by a 5000+ damage ardor or scathe :)