I wish there was an easy way to implement an SnK style team battle, I think folks discussed this in the past. You lock in a roster of 3 fighters in a PM to the TO, maybe you can change it up in between weeks, and then both players start with their first characters. When your character gets KO’d, move to the next character, drawing a hand of 7 cards. Play until one player’s characters are all KO’d.
You can sorta approximate this by rematching after a KO, then acting as though the winning character has the life total they ended the previous round with; they concede after losing that much health. Doesn’t preserve hands, though.