Jumbo Cactuar
Elemental: None
Starting Level: 20
Starting HP: 1766
Where do I get it? First you have to find Cactuar Island which is located to the east of the Centra Ruins. When you find it you'll see this little green thing that pops up on it every once in a while. This green thing is the Jumbo Cactuar. Use the Ragnarok to land on the island and chase down the Jumbo Cactuar. You have to beat it to get it as a GF.

GF Attack: 1,000 Needles: This attack is supposedly the second most powerful of the GF attacks in the game. The amount of damage it does is dependant on what level your Jumbo Cactuar is. It causes 1,000 points of damage for every ten levels of cactuar's experience so at level 100 the attack causes 10,000 damage. There's also no need for boosting this attack and its damage can't be reduced by high defense or magic.

Useful Abilities: Cactuar comes with five bonus abilties (HP bonus, Str Bonus, Vit Bones, Mag Bonus, Spr Bonus) which is cool but its so late in the game that it doesn't do that much to the character. He also has an ability that i think is useful called Move-HP Up which restores HP when you're walking on the world map.
Ability List
Ability

Eva-J
Luck-J
Magic
GF
Draw
Item
Defend
Kamikaze
Eva+30%
Luck+50%
Initiative
Move-HP Up
Hp Bonus
Str Bonus
Vit Bonus
Mag Bonus
Spr Bonus
Auto-Potion
Expendx2-1
GFHP+10%
GFHP+20%
GFHP+30%
AP Needed

200
200
Learned
Learned
Learned
Learned
100
100
150
200
160
200
Learned
Learned
Learned
Learned
Learned
150
250
40
70
140
Leads To...

Eva+30%
Luck+50%
Nothing
Nothing
Nothing
Nothing
Nothing
Nothing
Expendx2-1
Nothing
Nothing
Nothing
Nothing
Nothing
Nothing
Nothing
Nothing
Nothing
Nothing
GFHP+20%
GFHP+30%
Nothing