MagiMaster is the trickiest I've faced, reasons stated at above posts.

The first fight with Kefka (not the 'waiter' one), the one with teams, is one of the hardest imho. I'm always having one very weak group: Locke and Gau. Sabin goes with Cyan, Edgar and Celes (my Kefka strike force). Edgar just use Bioblaster at soldiers and when it come to Kefka, since my group has no real magic users, Celes can safely use Runic while the other single target Kefka with Aurabolt, Drill, Dispatch, etc.

[q=Big D]Atma Weapon was a walkover - first time I played through, I just 'Rasp'ed him into oblivion; on subsequent occasions, Vanish + Doom did the business. Some people say it's cheating, yet strangely I care not.[/q]

It's cheating.