Buddy suggested this one, having ponies run amok on Borderland 2's four main dlc trailers.

Audio from:
Captain Scarlett and her Pirate's Booty
http://youtu.be/PrQtO6mtmwQ
Mr Torgue's Campaign of Carnage
http://youtu.be/uWdeDm4qfd8
Sir Hammerlock's Big Game Hunt
http://youtu.be/2mSRW_Yscb8
Tiny Tina's Assault on Dragon Keep
http://youtu.be/pVWJ_eQ1lvo

With a brief extra sendoff using the GOTY Celebration Trailer
http://youtu.be/8bC1PLzNnRA