Mighty Smash is the best crossover counter in the game, and is a fantastic assist. Mighty Spark is a decent beam assist. I think he's a good team player. Mighty Smash even causes a hard knockdown. It leaves your opponent vulnerable so long that if you do OTG Flame Carpet + Mighty Smash, Dormammu actually has time to charge 3 Dark Spells and unleash 3D0C. To my knowledge, no other assist lets him do that. It would be interesting to try and run Thor/Strange and see what kind of utility comes from 3 Graces of Hoggoth being set up from Mighty Smash mid combo (you could blow all 3 Ms up for big damage, or set up 3 Ls for a laser).