User blog comment:Takeshi kun21/Tales of Fanon Mystic Arte Exhibition/@comment-24260323-20140503043227/@comment-8182065-20140503054219

2 is fine, in many games the characters usually have at least one, and a 2nd one unlockable after the first playthrough. And few games like Graces went up to 4, so I'd say 4 be the max (unless its like a unison MA where everyone in the party joins in/performs a mystic arte with a partner).

They can focus on single targets, have an aoe, and even have some buff/debuff/healing effects (depending on the character's skills of course). I'll edit that in a bit.