World of Final Fantasy - Fastest XG 2-Hit Kill, no damage taken

Now with fewer Tonberries!
Courage Under Fire x3 build: Fritt / Affrite / yellow Magna Roader, seeds are Meteor, Agi++.
Support stack: Werebat (Berserk) / Hyperion (Last Stand, SOS Haste) / purple Magna Roader (color coordinating), seeds are Bravery, Agi++.

Courage Under Fire x3 gives ~3.7x phys damage at low HP, which makes Meteor and Berserk attacks hit really hard. Not counting the random Evade & Counter hit, didn't want to re-roll it. You could play this a lot more conservatively with maybe an Auto Phoenix support instead of the buff sprinting and this would still be super fast. If he's still alive after the first Berserk hit, you can follow up with Haste. With Last Stand on both stacks, he will definitely die before you.

My double Meteor one is actually faster, but lacks style.

On the opposite end, killing Ultima Weapon with level 1 mirages:

Something something Diablos something something Behemonster