Skill is used in battle and don't use any MP. Rather then just inflicting damage, you can also trigger some effects on your opponents.

Abilitiy
MP
Effect on your opponent
Sleep Attack
5
Medium probabiliy of the sleep status effect (Three rounds)
Silence Attack
5
Medium probabiliy of the silence status effect (Three rounds)
Dark Attack
5
Medium probabiliy of the darkness status effect (Three rounds)
Sleep Buster
10
Very high probability of the sleep status effect (One round)
Silence Buster
10
Very high probabiliy of the silence status effect (One rounds)
Dark Buster
10
Very high probability of the darkness status effect (One round)
Zombie Attack
10
Chance of inflicting the zobie status effect
Tiple Foul
24
Chance of inflicting the sleep, silance darkness status effect
Delay Attack
8
Your opponent will drop slightlu in the CTB window
Delay Buster
18
Your opponent will drop far down in the CTB window
Power Break
8
Power break status effect - lowers an enemy's strenght
Maic Break
8
Magic break status effect - lowers an enemy's magic
Armour Break
12
Armour break status effect - lowers an enemy's defence and nulifies armoured
Mental Break
12
Mental break status effect - lowers an enemy's magic defence
Mug
10
Steals an iteam and inflicits damage - however the probabilty of success (initally 100%) is haved after each successfull robbery
Quick Hit
36
Attack quickly wih a very sort recovery period
Extract Abilty
1
Makes an enemy drop Ability Spheres
Extract Mana
1
Makes an enemy drop Mana Spheres
Extract Power
1
Makes an enemy drop Power Spheres
Extract Speed
1
Makes an enemy drop Speed Spheres
Nab Gil
30
Steals Gil
Full Break
99
Armour Break, Magic Break, Mental Breack and Power Break status effects

Command Abilities - Skill - Special - White Magic - Black Magic
Auto Abilities - Weapons - Armour