A mechanic where you can time your block and stun your opponent.
A Rubik's Cube style puzzle on a timer.OR! Like, one of those tile sliding puzzles.
It would be cool if there was something attached to combos. I remember when I first started playing this game years and years ago I found it odd that they would be all this flavor a text when your combo meter started going up like “wow” “amazing” “spectacular” but you never actually got rewarded for it. It would be cool if we got some small passes buffs every time we have, we reached a certain combo threshold with in a fight.
5-10% reduced cost for special attacks
6 star champs had adrenaline which gave us the option to heal back damage taken… what about if 7 stars had adrenaline but with the addition of burst damage on the opponent for every hit you deal to regain health.