I found these videos on the net awhile ago when I was looking at M.U.G.E.N matches. Mugen is a 2d fighting game where you can have any 2d video game character fight another. You can create your own fighters or download fighters other people have created. Mugen also lets you create the background stages and you can use any music you choose to. Creating your own fighters are tedious but fulfilling when its done. Most fighters if you follow the Marvel vs Capcom pattern, will need 200-300 frames of animation I believe (not positive). You have to create standing, walking, jumping, falling, laying down, crouching, special move, different level punches/kicks and super moves. If you don't have the time (months) to dedicate to creating, just download your favorite characters and rumble.
From what I have found the net, all these videos were created by PROXIDE
I just named them for this blog
Street fighter Vs Mortal Kombat-Worlds Collide
Street fighter Vs Mortal Kombat -AKUMAS Arc
Ken vs Raiden
Here are some M.U.G.E.N matches. These are not flash video these are actual game play
Ella (An original character, not mine)
Superman vs Thor
Wonderwoman