I couldn't miss the chance to practice my drawing!
Multi-targeting is a support ability in the Final Fantasy. Usually spells which have this attribute can have their multi-casting effect toggled, while other spells may forcibly effect an entire party.
Most spells can be multi-targeted by having the Materia attached to an All Materia. Mega-All makes nearly all spells and attacks multi-target. The multi-targeting attribute can be assigned to command abilities.
Having Mega-All equipped will immediately overwrite the attack with Slash-All even if the player has the double cut materia equipped, and they will only attack all enemies once. Mega-All is also incompatible with Quadra Magic, the screen will show that the player is targeting all enemies/allies but only one will be selected and all four castings of the spell will affect only that target.