Adel is a boss in Final Fantasy VIII, fought at the start of disc 4. Adel has Rinoa junctioned to her, and if the latter dies, it is Game Over. The battle is just beyond the point of no return, as the party refuses to exit the Lunatic Pandora without saving Rinoa.
Adel will frequently drain HP from Rinoa. She uses a host of powerful spells; first she will drain HP from Rinoa, then blast a character with Flare or Holy. Her Energy Bomber attack is a physical hit against one party member that can deal high damage if Vit is low. When "Magical powers are concentrated on Adel!" appears on the screen, her next spell will be Ultima that can do up to 3,000 damage, but its damage is halved by Shell.
If Gilgamesh is summoned into battle, he may kill Rinoa and the battle ends in a Game Over.
The player was originally intended to get 40 AP for defeating Adel. However, since there is no battle results screen after the battle, the player never receives it. Samantha Soul would have also been dropped, but instead it can only be mugged from the battle.
It is best to cast Regen on Rinoa at the start of the battle, followed by Shell, and be sure to Regen and Shell the party as well (Quistis's Mighty Guard works wonders). Rinoa has Regen spells to draw, which can be used for this purpose. Adel will frequently drain health from Rinoa, so one of the party should have the Recover command to occasionally top her up.
The player shouldn't use any multiple-target attacks in fear of hitting Rinoa. This rules out GFs and most Limit Breaks, especially the Renzokuken, because while it can deal a ton of damage to one target, some final attacks hit both Adel and Rinoa. One or two party member(s) should serve as the healer(s), topping up Rinoa and the party's health and protection. The player is free to use Zell's, Quistis's and Irvine's Limit Breaks; for Zell's, the player must not activate the finishing moves; for Quistis, the player can use Homing Laser, Gatling Gun, Laser Eye, or Acid; Irvine can use any ammo except Shotgun and Fire Ammo.
A quick way to win the battle is to use Cactuar's Kamikaze command that will likely kill Adel in one hit, depending on the character's current HP. If this method doesn't kill her, it should still cause significant damage and she can easily be killed from this point.