According to Reddit, the Launch Promo for Dragons of Tarkir will be Deathbringer Dragonlord!

Deathbringer Dragonlord (this name may be incorrect))

5BB

Rare

Creature - Dragon

5/6

Flying

When Deathbringer Dragonlord enters the battlefield, if you cast it from your hand, and there are five or more other creatures on the battlefield, then destroy all other creatures.

This creature looks to be a mainstay for Commander and one Hall of Famer has his eyes on the card for Standard:

Official previews for Dragons of Tarkir start on March 2nd.