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