Diablos (Magical Lamp) GF - FF8 Guide
The Magical Lamp is given to you right before the Timber Mission on Disc 1 by Headmaster Cid. If you fail to obtain this item now you'll miss it forever... and if you miss this item forever then you should restart your game, because Diablos is the only GF with the Enc-None ability (it means no random encounters).
Before attempting to fight Diablos you'll want to save your game at any Save Point. You can fight Diablos anywhere, all you have to do is open your inventory and use the Magical Lamp item. You'll be thrown into a battle with Diablos immediately after doing this.
Important Draw Notice: Make sure you Draw 100 Demi for each of your characters from Diablos. This is your first opportunity to get this Magic in the game.
The most important thing you need to do before fighting Diablos is junction Blind Magic to Selphie's weapon so when she attacks she will inflict Darkness on Diablos. Thankfully Diablos is weak to Darkness and it'll greatly decrease his accuracy for the entirety of this fight - which is the only way you can beat him right now.
For most of the fight Diablos will be using the Gravija and Demi spells. Gravija decreases your entire groups current HP by 75% and Demi decreases a single target's HP by 25%. These two spells on their own can't defeat anyone in your party but Diablos will also occasionally melee attack you too - which can defeat someone in your party... especially if they're very low health from his gravity attacks.
Tip: Make sure you have the Item Ability junctioned to all of your characters incase Diablos's melee attack defeats them. You'll need to Phoenix Down them so they can Draw all of their Demi Magic