Galactus is in Marvel vs Capcom 3. The confirmation of him being the final boss is not yet announced though but i think everybody else suspects him to be.
 
Here is a proof of his inclusion.
 

Here's a better proof of his appearance:
  

Holy cow sh*t!

" Holy cow sh*t! "

I think I just peed a little...I can't wait for this game

CONFIRMED! Galactus will make you fight two "heralds", bad guys from the game, at the same time before he will even fight you. Luckily they share the same health bar, because Galactus looks kind of hard...
 
  

" CONFIRMED! Galactus will make you fight two "heralds", bad guys from the game, at the same time before he will even fight you. Luckily they share the same health bar, because Galactus looks kind of hard...
 
  

More Marvel Vs. Capcom 3: Fate of Two Worlds Videos

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Hmmmm....I thought more people would find this as awesome as I do....

Another MVC boss who is actually unbeatable by every character in the game.