Leviathan
Elemental: Water
Starting Level: 17
Starting HP: 1349
Where do I get it? You have to draw this guy from the boss NORG during the battle at Balamb Garden in disk two.

GF Attack: Tsunami: A water based attack and one of the strongest ones in the game.

Useful Abilities: The most useful ability this guy comes with has to be Recover and its one of my most used abilties. Recover lets you restore a person's HP completely without using magic so its limitless. The Spr Bonus is pretty handy too.
Ability List
Ability

Spr-J
Magic
GF
Draw
Item
Mag-J
Elem-Atk-J
Elem-Defx2
Recover
Spr+20%
Spr+40%
Spr Bonus
Auto-Potion
SumMag+10%
SumMag+20%
SumMag+30%
GFHP+10%
GFHP+20%
GFHP+30%
Boost
Supt Mag-RF
GF Recov Med-RF
AP Needed

Learned
Learned
Learned
Learned
Learned
50
160
130
200
60
120
100
150
40
70
140
40
70
140
10
20
30
Leads To...

Nothing
Nothing
Nothing
Nothing
Nothing
Elem-Atk-J
Nothing
Nothing
Nothing
Spr+40%
Spr Bonus
Nothing
Nothing
GFHP+20%
SumMag+30%
Nothing
GFHP+20%
GFHP+30%
Nothing
Nothing
GF Recov Med-RF
Nothing