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