It's due out December 23rd on Xbox Live, for 400 MSP. It adds in total 12 medium, 9 hard and 2 extreme tiered challenges for fans.
"Trials HD is a full-featured, physics-based motorcycle racing game with over 50 mind-boggling tracks in two unique game modes," blurbs .
"Race Mode emphasizes balance, skill, and control as you tackle indoor obstacle tracks. Skill Mode features extreme stunt tracks in which explosions, crashes, and injuries cannot be avoided." It features a level editor to make your own tracks, and share them.
"Rev your engines with 35 new racing and skill tracks, over 50 new crazy physics objects, tournaments, new achievements worth 50 extra gamerscore, and more," goes the official press release for the Trials HD BIG Pack.
It releases "December 23 on Xbox LIVE Arcade at 400 points and is rated T for Teen by the ESRB. Fasten your helmet and prepare for serious bruises!" Check out the trailer.