C-c-c-combo!

A combat where you can earn power-ups to chain into a sick-ass combo. For each melee hit you put on a guy you get a "stack." These manifest as a flickering flaming aura, or little orbs of light, or etc.

You spend stacks to deal bonus damage, execute maneuvers, or apply effects. Maybe you have a character-specific damage type or condition you alone can apply.

Small creatures give fewer stacks (earn 1 per CR?). Landing a killing blow grants bonus stacks.

Stacks vanish at a rate of 1/round or something if you don't hit an enemy, or they all vanish after 3 rounds of no successful attacks.

Spend stacks for advantage on attack, to trip, to disarm, to grant advantage to an ally, do bonus damage, blind someone, stun them, push them back, get bonus movement, get multiple attacks in a round, do a whirlwind attack, etc. Must spend all stacks at once. Certain effects grant stacks back. E.g., if you have 20 stacks, spend 10 for a die of bonus damage and 10 for advantage, and hit, the advantage effect is refunding 10 stacks, plus the 3 you get for the hit (on a CR 3 creature). So you can, in theory, chain combos into bigger combos: spend for advantage, get more back, keep it going. Advantage every round til you have enough to spend for more damage or a major effect.