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