Here is the full list of all 37 Mayhem 3D achievements worth 1,000 gamerscore. It takes around 6-8 hours to unlock all of the achievements on Xbox 360.
Win 5 games in a single online session.
Win 3 games in a single online session.
Win an online demolition derby.
Win an online race.
KO an opponent with ramming speed (excluding challenge events).
Hit 4 opponents with a single ramming speed boost (excluding challenge events).
Win an exhibition event at insane difficulty (minimum 7 opponents).
"The Final Standoff" - Perfect Score
Complete the career.
Unlock all levels in the game.
Get 100% completion on the entire career.
Unlock all vehicles in the game.
Climb out of elimination position after seeing the crossbones.
Earn 100,000 mayhem points.
"A New Level Of Mayhem" - Perfect Score
Unlock issue 9, "The Final Standoff"
Use a stunned vehicle to push another vehicle into a pit (excluding challenge events).
Watch a saved replay in the replay theater.
"Unleash The Beasts" - Perfect Score
Collect 100 career stars.
Unlocked issue 8, "A New Level Of Mayhem"
"Mixed Up Mayhem" - Perfect Score
Unlock issue 7, "Unleash The Beasts"
Unlock all options in the game.
"Toro! Toro! Toro!" - Perfect Score
Unlock issue 6, "Mixed Up Mayhem"
Earn 20,000 mayhem points.
Earn 3,000 mayhem points in a single event (excluding challenge events).
"Blue Ribbon Brawl" - Perfect Score
Unlock issue 5, "Toro! Toro! Toro!"
Collect 20 parts in a single event (excluding challenge events).
"Date With Disaster" - Perfect Score
Unlock issue 4, "Blue Ribbon Brawl"
Collect 25 career stars.
"Dead Man At The Gorge" - Perfect Score
Unlock issue 3, "Date With Disaster"
"Rules of the Road" - Perfect Score