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