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
Got at least 5 seconds of air time
Bought all bikes
Earned $100,000 in cash
Played any splitscreen match
Got high score during Trick Session
Reached skill level 10
Scored first place in Rivals
Pulled a donut for at least 30 seconds
Unlocked all Iceland race tracks
Crashed while riding with at least 100 mph
Got dressed in a matching outfit set
Unlocked all Australia race tracks
Drifted 400ft
Unlocked all Egypt race tracks
Completed 3 Avatar FameStar weekly challenges
Bought your first new bike
Finished 5 bike club tasks
Reached skill level 2
You've won your first gold medal
Bought 1 new upgrade for any bike
Finished your first club task
Completed the tutorial
Reach skill level 20
Slipstream for 800 or more feet
Wheelie for 1,200 or more feet
Land a trick worth 20,000 or more points
Get a gold medal in every event
Seize the top spot on one of the club walls
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