Game Freak shed some more light on the collection of Pokemon in Pokemon X and
Xerneas is a Fairy-type, a new category of Pokemon being introduced in X and Y. This elk-like Pokemon is capable of casting Geomancy, an exclusive ability that causes rainbow-colored light to erupt from the ground and presumably kill stuff. Xerneas can also project a Fairy Aura to strength any Fairy-type moves used by Pokemon in that battle. This is a double-edged sword, though, because it can potentially strength enemy attacks as well.
Yveltal is a Dark- and Flying-type. Its exclusive move is Oblivion Wing, a flying attack that scorches the ground with red light. Dark Aura is similar to Fairy Aura except that it boosts the power of Dark-type moves.
Certain Pokemon will only be available in one game or another. For example, Xerneas is exclusive to Pokemon X while Yveltal is exclusive to Y. X owners will also get access to Swirlix, a Fairy-type that can prevent allies from being put to sleep and leech health from enemies with Draining Kiss. Instead of Swirlix, Y owners will get access to Fairy-type Spritzee. Spritzee can emit a sleep-inducing fragrance and learn the grass-type move Aromatherapy that removes allies' status conditions.
Many new Pokemon will be included in both games, though. For example, Inkay is a squid-like Pokemon with both Dark and Psychic powers. Inkay is capable of making enemies stop fighting for a period of time. Their Topsy-Turvy move will reverse any stat changes affecting a target. For example, Honedge's attack bonuses would suddenly become penalties. Inkay can eventually evolve into Malamar, said to be the most hypnotic Pokemon of all. Game Freak says that Malamar is used by "humans with ill intentions" to carry out their evil plots - perhaps a hint at the game's story. Malamar can use the ability Hypnosis to put enemies to sleep.
Another Pokemon shared between the two games is Pangoro. This fierce Panda is evolved from the adorable Pancham. Pangoro's Iron Fist ability boosts its punching attacks. It can pummel foes with the Hammer Arm ability. However, this move will also lower Pangoro's speed so it has to be used sparingly.
Pokemon X and Y will arrive this October exclusively on the 3DS. You can find more images of these new Pokemon at the game's website.