Yveltal

Yveltal (イベルタル) is the dual-type / Destruction Pokémon. It, along with Xerneas, are Legendary Pokemon of Pokémon X and Y.

Physiology
When Yveltal's arms itself in flight, it looks like the letter "Y".

Trivia

 * Yveltal is the fourth Pokémon to start with a Y, the others being Yanma, Yanmega and Yamask and the first Legendary to do so.
 * Yveltal is opposing Xerneus due to Xerneus representing life and Yveltal representing destruction.

Etymology
Its form may be a reference to Norse mythology guardians of the Yggdrasil Tree: a bird-like creature that protects the top of the tree, this may be Yveltal, a deer-like creature that protects the soil and trunk of the tree, this may be Xerneas, and a snake-like creature that protects the underworld below the tree. If this is right then there might be a snake-like legendary Pokémon to go with Xerneas and Yveltal. It may also be based off a wyvern.

Its name may come from the word tall since it can fly and start with the letter Y because it represents the Y axis in the 3D axis of X, Y and Z.