The absolute bestest combination. Ever.

You need:
-- The Mime class
-- !X-Magic
-- !Time (Lv6)
-- The 'Quick' spell
-- Mastered Summoner class for an Intelligence boost
-- The 'Bahamut' summon
-- The best Intelligence-boosting equipment you have
-- A Gold Hairpin (halves MP usage)

What to do:
-- Equip these three abilities, the equipment, and the Hairpin on a Mime.
-- Use !X-Magic and summon Bahamut once, then cast Quick on yourself. This will give you two extra turns where no one else can do anything.
-- Use !X-Magic and summon Bahamut twice for the first turn. Do the same thing for the second turn.

Add it up, and that will give you five Megaflares. That's pretty damn impressive. I suggest doing this for two of your characters. The other two should do nothing but feed these guys elixirs, because their MP will be wasted.