From Shoryuken Wiki, Marvel vs. Capcom 3 Strategy and More!

[ normal dodge : D while standing ] Character will dodge, and slide forward on the ground. Strong against Advance Attack, Jolts, and slow, mid hitting attacks. Weak against low attacks, multiple hit attacks, and possibly some higher or jumping attacks.

[ air (hop) dodge : D while crouching ] Character will hop into the air, and one normal can be executed. The normals are the same as jumping normals. Similar to hops or UOHs in other games. Can be used to start a combo. This will generally hop over lower attacks, but will lose to mid or higher attacks.

[ jumping dodge : D while jumping ] Character will become invincible for a short amount of time while jumping. Will also usually hover in the air for a little bit. Can be used after a jump attack, but no attack can be issued afterwards.

[ wakeup roll : D+direction while on the ground ] Character will roll either back or forward quickly after being knocked down. Character can be thrown during this. Most characters are also weak during the final frames of animation, however some characters (Bazoo) do not suffer this weakness as much. This cannot be executed after being hit with an I.Blow or OA.