Castlevania: Aria of Sorrow/Souls

Bullet Souls (Red)
These souls provide an attack ability, by pressing. They expend mana per use.

Guardian Souls (Blue)
Provides a guardian. Some can be toggled by pressing, while some will activate as long as you hold. It costs a given amount of MP per second.

Enchanted Souls (Yellow)
Provides a passive ability when equipped.

Ability Souls (Grey)
Select "Ability" on the start menu to activate/deactivate these abilities.