Here is the full list of all 37 Downslope achievements.
Have four players connected.
Reach the Highlands.
Reach the Burning Woods.
Reach the heart of the fire.
Reach the Desolation.
Reach the White Forest.
Reach the Ravine.
Reach the Wilderness.
Reach the Green Hills.
Reach the Desert.
Reach Metropolita.
Reach what lies beyond.
Go beyond.
Perform a Flawless run on 25 levels.
Perform a Flawless run on 50 levels.
Perform a Flawless run on 75 levels.
Perform a Flawless run on 100 levels.
Perform a Flawless run on 125 levels.
Perform a Flawless run on 150 levels.
Perform a Flawless run on 175 levels.
Perform a Flawless run on all levels.
Complete a race.
Complete 10 races.
Change all parts of a character's outfit.
Take off your helmet.
Do a trick 5 times on a run.
Crouch rapidly.
Do a run while touching the ground for less than 5 seconds.
Complete a run with less than a tenth of a second remaining.
Get burned 5 times in a single run.
Deflect three projectiles with a single spin.
Get struck by lightning at least 3 times in a single run.
Smash 5 of Patrice's totems on a run.
Successfully jump over a huge chasm in a Descent.
Complete all Forest trails without falling.
Stop and smell some roses.
Perform a Flawless run on all trails containing Rings.