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