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