How to get the Cactuar GF - FF8 Guide
Any time after obtaining the Ragnarok you'll be able to get the Jumbo Cactuar GF from Cactuar Island found in the southeastern most portion of the world (pictured below). If you've already been to the Cactuar Island Leveling Location prior to obtaining the Ragnarok you're already familiar with this place.
On the small island which you can only reach by using the Ragnarok you'll notice a Cactuar enemy popping in and out of the sand (pictured above). In order to begin the boss battle with the Jumbo Cactuar enemy you'll want to run into this Cactuar on the World Map.
Junction Tip: Junction Water to Elem-Atk and take Mug off of your character
Draw Tip: If you don't have many Meltdown spells in your stock, Draw some from Jumbo Cactuar
The first thing you should be aware of is Jumbo Cactuar likes to run away from battle if you leave him at 5% HP or lower for too long. You'll be notified when he is getting ready to flee with a message "Jumbo Cactuar is hesitating", he'll typically flee within a turn or two if you don't defeat him after this.
Jumbo Cactuar has anywhere between 33,000 - 330,000 HP depending on what level the monster is, so you'll want to be prepared for a very long fight when you decide to challenge him. The majority of his abilities aren't anything impressive but one you'll need to watch out for most is 10,000 Needles. He shoots 10,000 Needles at someone that all hit for 1 damage each, instantly defeating them.
Your best strategy will be to Draw-cast Meltdown at the start of the battle and Aura on your team if you have it to spare. Then just beat Jumbo Cactuar up with Limit Breaks whenever they're available and non stop melee attacks.