Jill Valentine is a downloadable character with Shuma-Gorath or available if you ordered the special edition.
Turns out, Valentine was already in the code and a hacker simply(?) replaced her code for Viewtiful Joe.
"I decrypted the PS3 version's executable file, changed some variables around, and replaced Viewtiful Joe with Jill. I then re-encrypted the executable and made a quick modification to the game-data MvC3 installs onto the PS3. (Namely, changed a parameter so that the game would treat the modified executable as though it were a patch.)"
"After a bit more tweaking and poking at the game files, I successfully loaded her into the character select screen. (And yes, she's completely playable, albeit at the expense of losing Viewtiful Joe.)"
While the character of Jill Valentine is fully playable - with all moves - the voice files are not on the game disc. Add to that, if you still want Shuma-Gorath (awesome!), you need to pay for the DLC pack.
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