Here is the full list of all 28 Defunct achievements.
Complete the story without dying or restarting in one session
You did it!
Get platinum in Time Trial on all maps
Get gold or higher in Time Trial on all maps
Complete the level "Into the Woods" without restarting or dying
Perform every trick once
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"
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
Find the secret spot in the level "Home"
Stay in the trash chute for more than 20 seconds
Complete Endgame
Complete Normal Mode
Complete Wasteland
Solve the level "Junkyard" in less than 3 minutes
Perform a trick in the air
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
Collect a collectible