First off, we have the starters in their second stages
Chespin's evolution will be called Hariboogu and is a pure Grass type:
Fenekin's evolution is called Teerunaa and is a pure Fire type, i am actually scared of this:
Froakie's evolution is called Gekogashira and is a pure Water type:
The mysterious Pokemon that was shown for a split second during the Pokemon Direct is called Torimian and is a Normal type:
Chigorasu is a new Rock/Dragon type fossil pokemon:
Amarusu is another new fossil pokemon of the Rock/Ice combination:
Nyaonikusu is a Psychic type pokemon that can be male and female:
Mewtwo gets another Mega Evolution called Mega Mewtwo X that is Psychic/Fighting , it is exclusive to Pokemon X:
Garchomp gets a Mega Evolution called Mega Garchomp:
UPDATE: CoroCoro has more information on the starter evolutions. Hariboogu will be known has the Thorn Armour Pokemon with the ability Overgrow. Teerunaa will be called the Fox Pokémon and it has the ability Blaze, and Gekogashira will be the Bubble Frog Pokémon and it will have the ability Torrent. A new pokemon was officially reavealed by the Pokemon Company, it is called Pyroar and it will be the evolution of Litleo, it is known as the Royal Pokemon:
Welcome to the Battle Tower. - Palmer