It looks like a puppetanimation. Maybe someone controls him with his own spiderweb ;)

fantastic work.. His left knee is a little distracting. I like playing as him, because of his Maximum Spider and SpiderSting moves.

 brilliantly fluid. can't find a thing to nitpick. ;3

 amazing 

The style is good, but the animation is lacking something. The movement's too wobbly, it gives the impression that's he's made of jello instead of the limberness his MvC idle has. I think it's how the limbs aren't synchronized in a logical way; e.g. his arms act the way you'd expect rubber prosthetics to behave.

 Fix the eye

 Eu fico aqui vendo ele se mover como uma gelatina.. D; 

Ooooh, neat. : )

 His right arm makes his posture appear a little bit weird. I like the wobbly animation other wise!

It's just the weird posture spiderman sometimes uses.

 In his Back, naturally

Great pixeling, but the anatomy is pretty weird. Where are the shoulders attached?

 You're certainly good at drawing him though, well done!