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