Here is the full list of all 41 MXGP2 - there are The Official Motocross Videogame achievements.
Win all the real events
Win a Monster Energy FIM MXoN using France
Become world champion in the MXGP class in Career mode
Win a race at Diamond Stadium 2, in any game mode
Win a race at Diamond Stadium 1, in any game mode
Win a race at Football Arena 2, in any game mode
Win a race at Football Arena 1, in any game mode
Win a Monster Energy FIM MXoN with any of the available nations
Win a race with an official MX2 rider, in any game mode
When a race with Pro Physics
Win a race with an official MXGP rider, in any game mode
Win a race with a Honda motorbike in any game mode
Win a race with a TM motorbike in any game mode
Win a race with a Yamaha motorbike in any game mode
Win a race with a Husqvarna motorbike in any game mode
Win a race with a Kawasaki motorbike in any game mode
Sign a contract with a team in the MXGP class in Career mode
Win a race with a Suzuki motorbike in any game mode
Complete a multiplayer Championship
Complete your first multiplayer race
Win a race at Glen Helen in Career mode
Win a race at Leon in Career mode
Win a race at Assen in Career mode
Win a race at Mantua in Career mode
Win a race at Lommel in Career mode
Win a race at Loket in Career mode
Win a race at Kegums in Career mode
Win a race at Uddevalla in Career mode
Win a race at Villars sous Ecot in Career mode
Win a race at Matterley Basin in Career mode
Win a race at Talavera de la Reina in Career mode
Win a race at Valkenswaard in Career mode
Get a Holeshot in any game mode
Win a race at Pietramurata in Career mode
Win a race at Neuquen in Career mode
Win a race at Nakhonchaisri in Career mode
Win a race at Losail in Career mode
Win a race at Teutschenthal in Career mode
Win a race with your custom team, in any game mode
Win a race at Maggiora in Career mode
Win a race with a KTM motorbike in any game mode