Here is the full list of all 28 Defunct achievements.
Perform every trick once
You did it!
Complete the story without dying or restarting in one session
Perform 2 tricks in the air without touching the ground
Solve the level "Junkyard" in less than 3 minutes
Complete the level "Into the Woods" without restarting or dying
Collect all collectibles
Find the secret spot in the level "Rock Bottom"
Find the secret spot in the level "Oasis"
Collect 30 collectibles
Collect 20 collectibles
Find the secret spot in the level "Into the Woods"
Stay in the trash chute for more than 20 seconds
Find the secret spot in the level "Home"
Perform a trick in the air
Complete Normal Mode
Complete Endgame
Complete Wasteland
Collect 10 collectibles
Reach max speed and keep it for 3 consecutive seconds
Jump 100 meters in the air
Complete Grasslands
Spend 5 seconds in the air without touching the ground
Collect a collectible
Get bronze or higher in Time Trial on all maps
Get silver or higher in Time Trial on all maps
Get gold or higher in Time Trial on all maps
Get platinum in Time Trial on all maps