To make any type of keyframes you need 3dstudio max and the alchemy artists pack.
And it's not easy even when you have them. As yet I haven't figured out the format for new keyframes, as I am still figuring out obvious stuff like making the weapons appear at the right time, bump mapping, mipmapping etc etc etc.
Hopefully, eventually all this stuff will get done, but it's still early days. A week ago I couldnt make any meshes for the game, now I can, so progress is being made.
I'll try to rotate the "built in" keyframes I supply with my meshes in future releases, and I'll (at some point) update and fix all the ones I've released so far.
Most of the characters you see in the background selection screens are where I have copied an existing mannequin and re-skinned it, which gives a stand-in mannequin, but the results aren't that great.
I'll be making new meshes for Quicksilver, Beast and Wanda at some stage, I hope. If not, and nobody else does it, I'll upload the converted XML2 versions.