Final Fantasy VII/Magic Materia

The magic materia is green. Usually, it has 3 to 5 levels (stars), and each time the materia gains a level, it's possible to use a new spell, with the first being equivalent to slight tickling, the second being the one you use most, and third one being the one that kills everything dead (or heals everyone alive or something). There are a few exceptions like Ultima. The first star filled at the beginning and the last star being filled means the materia is mastered, thus depending on the stars the materia can usually have 2 to 4 spells - in Ultima's case, only one.

Base magic is computed by multiplying 6 × (your level + your MP). For example, a level 20 character with 30 MP has base magic damage of 300 (6 × (20 + 30)). To find the amount of damage you'll do with a given spell, use the multiplier given with your base magic damage. Using the previous example, if the character cast Comet, he would do 1,500 damage (300 × 5).

Pairing magic with an All materia drops the damage done to 66.66% and using Quadra Magic drops it to 50% damage.

Contain
Note that pairing Contain with All has no effect.

Gravity
The Demi spells cause a lot of damage (particularly to fliers), but is not too accurate. Also, most bosses are nearly immune to Gravity effects as well. Effective against Emerald Weapon when used with W-Magic or Quadra Magic.

Master Magic
The Master Magic materia basically gives you all the abilities of all the magic materias. It can be gotten either by defeating Emerald WEAPON and trading in the Earth Harp at Kalm, or by mastering all the magic materias and trading them for the Master Magic materia at Cosmo Canyon (if you managed to save that Huge materia anyway). The Master Magic materia can be linked to and "All" or a "Quadra Magic" materia to give all spells the effect of the support materia.