Here is the full list of all 50 Monster Energy Supercross - there are The Official Videogame achievements.
Complete any one of the SX Challenges
Reach the podium in the 450 Championship in Career mode
Race a total of 300 miles (482 km) with any bike
Sign a contract with any 450 Sponsor in Career mode
Earn a total of 3,000,000 SX Credits
Complete a total of 30 Main Events in a Custom Track created by other players
Complete a total of 10 Main Events in a Custom Track created by other players
Create a total of 5 Custom Tracks
Win a total of 50 Main Events in any game mode
Race a total of 150 miles (241 km) with any bike
Reach Prestige Level 100
Earn a total of 1,500,000 SX Credits
Win a 450 Championship with R. Dungey in Official Mode
Get a total of 10 Holeshots in any game mode
Win a total of 25 Main Events in any game mode
Pass a Last Chance Qualifier session in any game mode
Make 50 successive jumps without taking a fall or using Rewind in Time Attack mode
Reach the podium in the 250 East Championship in Career mode
Win a Main Event at East Rutherford in any game mode
Win a Main Event at St. Louis in any game mode
Reach Prestige Level 50
Win a Main Event at Detroit in any game mode
Race a total of 50 miles (80 km) with any bike
Create your first Custom Track
Win a Main Event at Indianapolis in any game mode
Win a Main Event at Daytona Beach in any game mode
Earn a total of 500,000 SX Credits
Win a Main Event at Toronto in any game mode
Win a Main Event at Atlanta in any game mode
Win a Main Event at Minneapolis in any game mode
Reach the podium in the 250 West Championship in Career mode
Win a Main Event at Las Vegas in any game mode
Win a Main Event at Salt Lake City in any game mode
Reach Prestige Level 25
Win a Main Event at Seattle in any game mode
Win a Main Event at Arlington in any game mode
Win a Main Event at Oakland in any game mode
Win a Main Event at Glendale in any game mode
Win a Main Event at San Diego in any game mode
Get a Holeshot in any game mode
Win a Main Event at Anaheim 1 in any game mode
Complete a race without using Rewind in any game mode
Complete a race with Normal Physics in any game mode
Complete a race without taking a fall or using Rewind in any game mode
Make your first purchase in the rider customisation page
Complete a Main Event in a Custom Track created by another player
Create your Custom Rider
Win a Main Event at Anaheim 2 in any game mode
Complete a race without taking a fall in any game mode
Win a Main Event in any game mode