Offensive Black magic spells can sometimes fell an opponent with a single blow. Black magic almost uses up MP. Bear in mind your opponents elemental characteristics so that you can select the most appropriate spell..

Abilitiy
MP
Effect
Fire
4
Causes slight fire damage
Fira
8
Causes medium fire damage
Firaga
16
Causes heavy fire damage
Thunder
4
Causes slight lighting damage
Thundra
8
Causes medium fire damage
Thundaga
16
Causse heavy fire damage
Water
4
Causes slight water damage
Watera
8
Causes medium water damage
Waterga
12
Causes heavy water damage
Blizzard
4
Causes slight ice damage
Blizzara
8
Causes medium ice damage
Blizzaga
12
Causes heavy ice damage
Bio
10
Poison status effect
Demi
32
Reduces HP by 25%
Death
20
KOs a character outright
Drain
12
Drains HP
Osmouse
0
Drains MP
Flare
54
Heavy non-elemental damage
Utima
90
Heavy non-elemental damage

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