[quote=@spiderfucker]
[@KoL] ah, then i stand corrected.
[/quote]

Actually, I just recalled now,that really there should be no limit on duel modes, since the final showdown against Noumi was a 3 v 1 (Lime Bell, Cyan Pile and Silver Crow vs Dust Taker), but since they were also on the UNF, there was the possibility of parties not involved on the duel to disturb the fight, which is what happened with Black Vice and Black Lotus' appearances.

Which makes me conclude that there's no limitation to duels on Brain Burst other than the Duelists own morals. And, in the UNF, all is fair game, for real.