As far as potential character DLC is concerned, assuming they don't make it in: Captain Toad, King K. Rool, Impa, Ridley***, Hades, Dark Pit, Krystal, Black Shadow, Mewtwo*, Blaziken, Roy*, Lucas*, Isaac, Wonder Red, Snake**
* Returning veterans
** May only happen if Sakurai decides to honor Kojima's recent request (and if Snake indeed gets his trophy)
*** Even if Ridley is just a boss, the Ridley that is fought in Other M isn't the real Ridley but a clone. This could likely be the case yet again in Pyrosphere. Besides, couldn't it just be excepted that the two Ridleys would look different and have different sizes?