The final form of Ultimecia is the final boss of Final Fantasy VIII. After her Guardian Force, Griever, is destroyed, Ultimecia emerges from the void in her most powerful form, ready to complete time compression. Ultimecia is in the process of absorbing all time, space, and existence and stars and planets from across the space/time continuum are being sucked into her body. The theme of the battle is "The Extreme."
Once she reveals her lower half, Ultimecia drawsApocalypse from it and begins to cast it upon the party. Apocalypse is a spell even more powerful than Ultima, and it can cause damage in the range of 8,000 HP or higher if the party is not protected by Shell or invincibility.
When Ultimecia's lower half is revealed, she will only use Hell's Judgement, Destroy Stocked Magic, Absorbed Into Time, Draw Apocalypse, and Apocalypse. She will often cast Draw Apocalypse after using Hell's Judgement.
After Ultimecia uses her first Apocalypse spell, the party can attempt to stop Ultimecia from using it by destroying Ultimecia's lower half. If her lower half is destroyed Ultimecia will begin to cast powerful Ultima and Meteor spells and might cast Ultima or Meteor right after using Hell's Judgement.
When Ultimecia begins speaking she has run out of HP but the party must attack her to make her say her next line. She can still attack the party at this point. Upon her defeat, Ultimecia will fall, exploding in a massive sequence of colorful light.
After Ultimecia reveals her lower half, healing the party or using a Holy War is crucial, because she may cast Apocalypse instantly after drawing it. A good strategy to defeat Ultimecia's lower half is to have Irvine on Aura, and pound away with Armor Shot.
To defeat Ultimecia, the party best stick with Limit Breaks for everybody except perhaps Selphie. It is wise to have Selphie as the healer, and she can also Triple-cast Ultima until Ultimecia reveals her lower half. Once Ultimecia's lower half is a target, Selphie can draw Apocalypse from it and then Triple-cast it back on Ultimecia. If her lower half is destroyed, the player should heal everybody to avoid being killed by Meteor or Ultima on her next turn.
A quick way is to have all three of the party members stand by until she uses Hell's Judgement. With everybody's HP at one, two characters can use Limit Breaks while the last heals either by Triple-Casting Curaga, or using a Megalixir (or via White Wind, if the third party member is Quistis). There is little risk in this strategy before Ultimecia reveals her lower-half because her only other attacks are single-targeting. It is unnecessary to use Hell's Judgment to gain Limit Breaks as long as the player can keep the party in Aura status, but Ultimecia might destroy all of the Aura magic in the party's inventory. If Quistis is in the party when Hell's Judgement is cast, a good idea is to have her cast Mighty Guard which—with all party members at 1 HP—will likely cast Haste, Regen, Float and Aura in addition to Shell and Protect.
When Ultimecia begins her final speech, only regular attacks are needed to make her say her next line, but she can still attack the party at this point.
Part of the field of stars in the background during the fight is actually part of Ultimecia herself, emphasizing she is absorbing space and time during the fight. When viewed in a third party program and during some attack animations when the camera zooms out far enough, the edge of her dress can be seen extending under and behind the party, the underside red to match the rest of her outfit.
The Final Fantasy XaeonAnima resembles Ultimecia's final form, as the two have an upper and a lower part, and Ultimecia's lower part is displayed in a similar position to Anima's upper part.