Mega Man and Pacman have been confirmed as characters in Street Fighter X Tekken and will be exclusive to the PlayStation 3 and Vita, that's as well as Infamous hero (or villain) Cole MacGrath. Mega Man is based on his original art work look and is looking a bit worse for wear. That is until you see him move, at which point you see exactly what he's capable of.
Pacman sits happily atop Mokujin, a wooden character that originates from Tekken 3 and copied the style of other characters. He occasionally jumps off when the enemy is standing close but most of his moves are from his "robot," and utilizing Iron Man-like beams will be key to winning, I think.
The top video also shows other PlayStation exclusive characters: Kuro, Toro and Cole. All of this makes the PS3 or Vita versions of the game the ones to go for, although it wouldn't surprise me to see Pacman and Mega Man as DLC on the 360 at some point going forward. Part of me wonders how Microsoft are dealing with this – they don't enjoy it when Sony get exclusive content for a multi-platform game and this is a lot of exclusive content – but perhaps we'll see exclusive content for the 360 when Tekken X Street Fighter starts to be detailed.