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