I haven't taken the time to master the inputs for the flame carpet juggles on small characters. I'm focusing my training time on movement during flight and getting Morrigan's bnb down. I just stumbled across a really nice bnb for Dormammu that works on anyone with my team in corners:
j.S, c.LHS, sj.H, fly, j.LH, Dark Hole L, j.HS, Flame Carpet + TK Overdrive, Dark Matter, Dark Matter x Dark Hole, Chaotic Flame -> Astral Vision, Soul Drain, fly, j.S, Shadow Blade H, fly Shadow Blade H.
Then there's the combo that does 840K for 1 bar:
j.S, c.LHS, sj.H, fly, j.LH, Dark Hole L, j.HS, Dark Spell L, Flame Carpet + TK Overdrive, Dark Matter x Dark Spell M, s.S, 1D1C, Purification, Chaotic Flame
It's really hard to do consistently, though. Lots of awkward links.
So, I'm always developing tech and practicing new stuff, but a combo that only works on small characters is pretty low on my priority list. If I'm fighting Wolverine I'm generally trying to run the hell away since rushing him is suicide vs. drill claw and dive kick, and because he tends to be backed by tatsu assist which >>>> all of Dormammu's normals (seriously, an Akuma spamming Tatsu > all of Dormammu's tridash attacks in front and behind).
Dorm seems pretty mobile to me. Tridashes, teleports, flight...the only thing that sucks about his mobility is his ground dash.
It can be weird using multiple characters with air dashes, because the trijump angles are different. Like, I can use Dormammu, Phoenix, and Morrigan just fine, but I can't use Storm for crap because I always get her j.S angle wrong, and I whiff Trish's j.S all the time. It can take a lot of work to get a feel on the different superjump speeds, air dash speeds, hitboxes, and proper angles, and sometimes using 2-3 characters with similar abilities messes you up. At least that's my experience.