Omega sentinel - her debuffs will pause for 10 seconds instead of 7, and sp1 Refreshes incenerates as well.
Winter Soldier: When defending, Winter Soldier is more aggressive. But it would have to be applied in RoL so that speed-testing champions against him was more fun.
Beast! I think only a few people are aware that Beast is one of the best power controllers in the game, he's also bleed resistant and able to regenerate. Maybe Kabam could add prowess abilities linked to powerful bleeds, just a little push to make him competitive.
Omega Red's synergy with Sabertooth should be in his base kit
Zemo can cleanse stuns
Proxima Midnight should start the fight with all her missions to complete at the same time
Yellowjacket to join his brethren at being buff immune.