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 their 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 Adel.
It is best to cast Regen on Rinoa at the start of the battle, followed by Shell, and be sure to cast these spells onto the party as well (Quistis's Mighty Guard and Selphie's Wall work 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 (recovery items can also be used).
The player shouldn't use any multiple-target attacks in fear of hitting Rinoa. This rules out GFs and most Limit Breaks, including 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. Though Selphie's The End engulfs both Adel and Rinoa, it will only kill Adel.
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. The user being sacrificed does not matter for this battle, as there are no battle spoils anyway.
If the party doesn't have Kamikaze, then they should cast Meltdown on Adel and hack away at her. Though most GFs cannot be used, the party can summon Cerberus to help with quick buffing and healing, and for triple-casting single-target spells onto Adel. Haste is also useful to triple-cast onto the party to keep up with both attacking and healing. If the party managed to draw any Aura spells from the previous boss, now is a good time to use it on either Zell or Irvine.