I played this today for hours.
Some things: everyone out here is using X-23, and for good reason, she is an absolute monster. She doesn't have an airdash but she doesn't even need it when she can get to you and the other side of you in no time at all.
Good luck getting in on Arthur. Doom's Rocks are still his best assist and my brother was doing sick **** using Haggar's lead pipe in the air with Doom rocks to approach people. Also, Haggar does MONSTROUS damage and doesn't seem as slow as many bulky characters because he has nice ways to get in. His assist is also definitely Psylocke-esque and you can't hit him DURING the actual lariat it seems but only after it when he stands there and poses.
Storm's Hail Storm does an un-neccesarily large amount of chip damage and there is even less lag time between when one ends and when you can do another, if you have 3 meters and even if your opponent just blocks all 3 they'll probably take a good 35% or more life. Also, I know assist characters take double damage, and that Arthur has low health but I was playing a guy and I hail stormed as he called out Arthur(who was at full health) and it killed his Arthur so...yeah. Storm def looks like the best of the returning big MvC2 3.
No one used Magneto. No one used Phoenix. No one used Taskmaster or Tron Bonne either really. Wesker's maximum wesker super is dumb and kind of spammable because though it has some recovery lag, he usually lands too far from you to be able and go and punish him, plus it does good chip. Zero probably has the best rushdown game of anyone out there.
I know I'm forgetting some things, I'll try to post more when I wake up and can remember.