The Mechromancer will be developed after work on Borderlands 2 is finished and the game is in certification
Gearbox Software has unveiled that a new playable class will be added to Borderlands 2 after the development of the game will be finished. Part human and part machine, Mechromancer will be available as a free download to members of the Borderlands 2 Premiere Club, which you can gain access to by pre-ordering Borderlands 2 from a participating retailer. The Mechromancer will also be available as premium downloadable content for those who aren't Premiere Club members at the same time.
Also, a compatibility update will be released so that people who have the Mechromancer can play with those who don't.