The Undying

From Final Fantasy - Wiki on Neoseeker

The Undying is the final incarnation of Vayne Solidor and the final boss battle of Final Fantasy XII.

Level	HP	MP	STR	MAG PW	VIT	SPD	ATK PW	DEF	MAG RES	EVA	EXP	LP	CP	GIL
55	228299	999	51	35	87	23	90	38	33	0	0	0	0	0

Steal: Dark Matter

Strategy

This is it. The Undying can be a very difficult boss fight as you would expect from the final battle of the game. Come in with equipment that blocks status effects, and have your gambits to heal them high. He’ll cast Megaflare which is a powerful area attack, so staying close is risky. You can employ ranged attacks or the hit-and-run strategy for your front-line fighter. You might notice that he has no health bar to indicate how much HP he has remaining, but every time you knock off a quarter percent he throw up a new barrier, making him immune to either physical or magickal damage. For the physical immunity, cast your best magicks (Scathe or Flare) over and over. For the magick barrier, cast Bravery and attack like mad. Once he hits 25% of his HP, The Undying will have barriers that block any damage, which will last for a while. At this point, run away from him and heal up as best you can. Feel free to use any leftover items to recover MP or HP. Once the barriers drop and since this is the end of the line, use your Quickenings to really hurt him. When he finally falls, you will be able to witness the final scenes of the game.