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.
Played any splitscreen match
Slipstreamed for 800 or more feet
Pulled a wheelie for 1,200 or more feet
Pulled a donut for at least 30 seconds
Landed a trick worth 20,000 or more points
Scored a slingshot distance of 2000ft
Got dressed in a matching outfit set
Bought all bikes
Earned $100,000 in cash
Got at least 5 seconds of air time
Unlocked all Iceland race tracks
Reached skill level 10
Unlocked all Australia race tracks
Got high score during Trick Session
Finished your first club task
Seized the top spot on one of the club walls
Drifted 400ft
Unlocked all Egypt race tracks
Crashed while riding with at least 100 mph
Scored first place in Rivals
Bought 1 new upgrade for any bike
Bought your first new bike
Reached skill level 2
You've won your first gold medal
Completed the tutorial
Completed 3 Avatar FameStar weekly challenges
Reach skill level 20
Get a gold medal in every event
Finish 5 bike club tasks
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