Here is the full list of all 20 Antigraviator achievements.
You lapped someone
Break the soundbarrier
Finish your first race
Win an online race
Do not die during a race
Finish your first League
Finish the Legends League
Buy your first item
Buy all items
Set 500 traps that get triggered
Win a race with second place finishing within 0.5 seconds of you
Keep a constant speed
Play 400 quick races
Compete in 400 death races
Play 400 countdown races
Play all the maps in the game
Unlock the X1Z1
Unlock the crocco
Avoid taking damage during a race
Make the bridge jump in Serpentine Valley