Here is the full list of all 36 MXGP3 - there are The Official Motocross Videogame achievements.
Cover a total of 300 km (186 miles) with any bike
Purchase at least one custom bike from each manufacturer
Win a Monster Energy FIM MXoN with any of the available nations
Win a Monster Energy FIM MXoN with France
Sign a contract with an Official Team of the MXGP class in Career mode
Win a race at Glen Helen in Career mode
Win a race at Charlotte in Career mode
Win a race at Assen in Career mode
Win a race at Frauenfeld-Gachnang in Career mode
Win a race at Lommel in Career mode
Win a race at Loket in Career mode
Win a race at Mantua in Career mode
Cover a total of 150 km (93 miles) with any bike
Win a race at Saint-Jean-d'Angély in Career mode
Win a race at Talavera de la Reina in Career mode
Win a race at Pietramurata in Career mode
Win a race at Teutschenthal in Career mode
Win a race at Leon in Career mode
Win a race with Pro Physics in any game mode
Get 10 Holeshots in any game mode
Win a race at Neuquen in Career mode
Get a Holeshot in any game mode
Make your first purchase in the rider customisation page
Win a race at Valkenswaard in Career mode
Cover a total of 50 km (31 miles) with any bike
Win a race at Suphan Buri in Career mode
Win a race at Losail in Career mode
Win a race at Matterley Basin in Career mode
Win a race without using the Rewind in any Single Player game mode
Win a race at Kegums in Career mode
Win a race without taking a fall in any game mode
Win a race with your Custom Team in any game mode
Use the Rewind for the first time
Fall for the first time
Win 50 Grand Prix in any game mode
Become world champion in the MXGP class in Career mode