In Marvel vs. Capcom 3: Fate of Two Worlds for the PS3 and Xbox 360, there are a total of four characters you can unlock with the regular version. If you paid an extra ten bucks for the Special Edition of the game, then you will have early access to Jill Valentine and Shuma Gorath, which will be released on March 15th 2011 as DLC content.
To unlock characters, you simply need to accumulate PP (player points) which is earned during arcade mode, multiplayer fights, and during training mode, with arcade mode generally being the easiest to earn them in. You don’t have to spend PP on characters, you just have to get enough PP and they’ll unlock automatically.
Here are the unlockable characters, and how much PP they require to unlock:
Akuma — 2000 PP
Hsien-Ko — 6000 PP
Sentinel — 4000 PP
Taskmaster — 8000 PP
If you’re trying to unlock all of the characters as quickly as possible, I would suggest playing on the Very Easy difficulty in arcade mode, since you’ll be able to complete it in about 15 minutes and gain between 2000 to 3000 PP on each playthrough. Harder difficulties don’t grant you more PP, so this will most likely be your quickest way to unlock all of the characters.