Here is the full list of all 19 2XL Supercross achievements.
Complete a Supercross race
Win your first Supercross race
Play for one hour total
Play for two and a half hours total
Play for five hours total
Play for ten hours total
Spent one hour in the air total
Fly one mile through the air total
Ride ten miles total
Ride fifty miles total
Ride one hundred miles total
Complete one Time Trial lap
Complete five Time Trial laps
Complete ten Time Trial laps
Improve on your fastest Time Trial on three consecutive laps
Win three Supercross races in a row
Preload five times in a single race event
Land a backflip in a race you come in first place
Complete 10 events