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.
Drifted 400ft
You've won your first gold medal
Reached skill level 2
Completed the tutorial
Completed 3 Avatar FameStar weekly challenges
Played any splitscreen match
Reach skill level 20
Buy your first new bike
Buy all 6 bikes
Get dressed in a matching outfit set
Unlock all Egypt race tracks
Unlock all Australia race tracks
Unlock all Iceland race tracks
Reach skill level 10
Earn $100,000 in cash
Score first place in Rivals
Crash while riding with at least 100 mph
Get at least 5 seconds of air time
Donut for at least 30 seconds
Slipstream for 800 or more feet
Wheelie for 1,200 or more feet
Get high score during Trick Session
Land a trick worth 20,000 or more points
Score a slingshot distance of 2000ft
Buy 1 new upgrade for any bike
Get a gold medal in every event
Finish your first club task
Seize the top spot on one of the club walls
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