Move degradation, like Smash Bros. had. I've yet to see a valid argument as to why it wouldn't work, or wouldn't be anything less than beneficial for the game. It promotes variety, and it'd make matches a lot funner to play.
Sackboy spam? Kratos chain-grab? Radec's sniper? Sly Thunder Roll? Sweet Tooth's shotgun? People love to spam whatever they can get away with (and in FFA, there's a lot they can get away with). Just make the AP-gain gradually lower the more someone uses the same move in a row. They're free to spam it as much as they like, they're just rewarded less for doing so.
It works flawlessly for Smash Bros. Perhaps I'm not thinking it through enough (from a technical point of view) for All-Stars, but again, I don't see why it wouldn't work just as flawlessly here.
Note as well that I'm not the one who came up with this, it's just something that was brought up before the game's release and something I strongly agree with.
Also, I'm a black belt in FFA, I've more than dealt with my own share of spam the old fashioned way thank you. :3
I just want Card Sagas Wars. Seriously, I'd do anything, just give me Card Sagas Wars. Please. PSN:ChocoboDreams