Full list of all 36 Motocross Madness achievements worth 500 gamerscore. It takes around 8-10 hours to unlock all of the achievements in the base game.
The base game contains 30 achievements worth 400 Gamerscore, and there is 1 DLC pack containing 6 achievements worth 100 Gamerscore.
Scored a slingshot distance of 2000ft
Slipstreamed for 800 or more feet
Earned $100,000 in cash
Got high score during Trick Session
Got dressed in a matching outfit set
Crashed while riding with at least 100 mph
Got at least 5 seconds of air time
Bought all bikes
Reached skill level 10
Unlocked all Iceland race tracks
Drifted 400ft
Pulled a donut for at least 30 seconds
Unlocked all Australia race tracks
Seized the top spot on one of the club walls
Scored first place in Rivals
Completed 3 Avatar FameStar weekly challenges
Unlocked all Egypt race tracks
Bought 1 new upgrade for any bike
Bought your first new bike
Finished 5 bike club tasks
Reached skill level 2
You've won your first gold medal
Finished your first club task
Completed the tutorial
Reach skill level 20
Play any splitscreen match
Wheelie for 1,200 or more feet
Land a trick worth 20,000 or more points
Get a gold medal in every event
Collect all skulls around the world
Win all the Trick Jams events
Win all the Stunt Race events
Perform an X, Y and B combo within one event
Unlock 5 Trick Jam skills
Unlock all 10 Trick Jam skills
Drift for 2,000 or more feet on any of Trick Jam tracks