I say the best summon is one you can't use normally during the game. It's Alexander, which Eiko & Dagger summon to prevent Bahumut from doing anymore damage. Although Garland comes in with the Invincible & somehow drains it's power... Then he starts to take off with it & destroys Alexandria, just as he did Madain Sari. This is truly bad. So of a real summon I have to say Pheonix, as if you have enough of it's gems it'll come save your butt (as long as you have Eiko in battle.) from your knockout status for all of the Characters, although it's extremely rare during random battles, it'll occur in tough boss battles more commonly.
Thanks- BudSoda02 BudSoda02@yahoo.com
