As per tradition right around the release of CoroCoro, Pokemon X and Pokemon Y are getting a slew of rumors regarding Pokedex additions with new dual-types and a few potential evolutions of pre-existing Pokemon.

Originaly gathered from 2Chan, Pokejungle reports the following rumor updates...

Panpura (Grass/Ghost) is a pumpkin ghost Pokemon possibly based on Jack 'O Latern.

Yotsurun (Ice/Fighting) is a giant with a horn who likes to use the move Ice Hammer. Could this another potential Snorlax where the Pokemon towers over the trainer?

Syoomai (Water/Bug) the snail-like evolution of Shellos where the little bugger finally gets a shell. If fans recall from Pokemon Diamond and Pearl, Shellos has an evolution called Gastrodon (Water/Ground). This may become an Eevee or Oddish scenario where trainers have more than one evolution path to choose from.

And lastly, the final rumored Pokemon is Myuujii (Psychic), a Pokemon that is based on that quarter note who, no doubt, uses sound related moves.

Keep in mind that with rumors from places like 2Chan and forums in general, only a percentage of the rumors wind up being true. From what we've seen so far, it would not be surprising if new dual-types like Grass/Ghost are introduced, but Nintendo and Game Freak have been hesitant to release any new evolution of pre-existing Pokemon.

Only time will tell whether these Pokemon will be included in the X and Y Pokedex.