Ultimecia will express her fury at SeeD for interfering with her plans of time compression, before she engages you in combat. The participants are picked randomly (including Squall), so make sure your GFs are evenly spread out. Ultimecia removes fallen companions in battle with her Angel move, but if you’re quick enough you can beat her to it with a well-timed Full-life spell. She comes in 5 forms, which you’ll have to fight consecutively. Use Hero’s Medicine for an easy victory if you want to (it’s the final battle, anyway).

Should Squall be chosen as one of the participants (which occurs quite frequently, actually), I suggest letting him do all the attacking. The rest should simply support him by casting Meltdown to destroy the enemy’s defense and heal when needed.

BOSS >> ULTEMECIA
HP: 43,000 Weakness: Poison Strength: Holy
AP: 0 Draw: Haste, Slow, Reflect, Demi

Strategy: The 1st form of Ultimecia can be taken down effortlessly with a single Meltdown, Aura-Renzokuken combination. However, I suggest you make use of this one to prepare for the upcoming battles; put everyone in Triple, Protect, Shell, Haste and Regen status, followed by Aura if possible. Ultimecia will attempt to spoil the party with Quake, and her Maelstrom causes status maladies and heavy HP damage to all, but counter that with a Megalixir.

BOSS >> GRIEVER
HP: 120,000+ Weakness: --- Strength: Earth, Poison
AP: 0 Draw: Bio, Quake, Tornado

Strategy: Griever has a status ailment attack, tends to cast Demi’ and Doom, and has an annoying habit of drawing spells from your party. Counter Doom with either a Remedy Plus or a Megalixir and hit him repeatedly with Renzokukens (remember to reduce his defense to zero with Meltdown first). Casting Ultima coupled with Triple works well, too, but I suggest you learn Eden’s Expendx3-1 character ability first.

Griever will occasionally remove an entire set of spells from your magic list, thus forcing you to lose that junction (i.e. if you’ve junctioned Full-life to HP, it’ll fall back to its original value).
Also note that from Griever onwards, the bosses have the ability to kill off any of your GFs in a single blow, so don’t bother with summoning them. Griever will use his Shockwave Pulsar at the end (or earlier if you aren’t quick enough in taking him out), which takes about 3,000 HP from everyone or 1,500 if you’re under a Shell condition.

BOSS x 2 >> ULTEMECIA-GRIEVER / HELIX
HP: 180,000+ / 25,000+ Weakness: --- Strength:
AP: 0 Draw: Firaga, Thundaga, Blizzaga / Esuna, Dispel

Strategy: Ultimecia will junction with Griever for a truly nasty package. This 3rd form likes to cast Tornado, Meteor and Holy, plus she’ll occasionally remove an entire set of spells from your magic list. She’s also capable of casting Shockwave Pulsar at any time. Other than that, tiny cronies will appear to help during the fight. If 2 Helixes appear, watch out for Ultimecia’s Great Attractor, a physical attack that does 4,000+ damage to the entire party. Stick to the tried-and-true Meltdown, Aura-Renzokuken combination to take her down. If she detaches a part of herself, it means she’s close to defeat—keep it going!

FINAL BOSS >> TRUE ULTEMECIA
HP: 250,000+ / 16,000+ Weakness: --- Strength: ---
AP: 0 Draw: Holy, Flare / Apocalypse

Strategy: Ultimecia, in her final form, has more offensive moves at her disposal: Hell Judgment can bring everyone down to 1 HP (use a Hero’s Medicine on Squall and have him launch his Renzokuken repeatedly).

She’ll also cast Ultima, Flare and Holy. When her lower body appears during the course of the fight, she’ll draw Apocalypse from it, which hits the entire party for roughly 3,500+ worth of damage. Take note that you can do the same to her, by drawing Apocalypse first. Ultimecia retains the annoying ability to remove an entire set of spells from you, too. Simply keep the Meltdown, Aura-Renzokuken combinations coming and heal immediately when she hits you with a Hell Judgment— she might cast Ultima as her next move. Try to dispose of her lower body first when it appears.

When Ultimecia is near defeat, she’ll start uttering lines in battle. During this period, you have to pound on her until she finishes what she has to say; each attack usually results in her speaking another line. Only when you’ve seen all she has to say can you strike the finishing blow.

Enjoy the ending!