Here is the full list of all 31 WayDown achievements.
You beat the game!
You've bested Crossfit Satan! I wonder if he was the mastermind of your curse?
Broke the seal, and stepped into Hell
Bested the speaker for the trees, who was silenced long ago
Bested that totally normal and not at all weird deer
Uncovered the unnatural, subterranean Forest
Bested the Stranded Chuul
Bested the lvl 2 dwarven fighter's worst nightmare
Uncovered the Arcane Ruins
Bested Charlie the Rat King
Bested Phleshy, the Flesh Golem
Bested the tallest hairdo in all the Axis Powers
Rescued the squad Trigger Finger
Uncovered the Cursed Mines
Bested the foremost combat expert in the Reich
Rescued the squad People-Fixer
Bested the circus trained SS Officer
Rescued the squad Minister
Rescued designated Boom Expert
Rescued the squad Projectile Trajectory Expert
Accessed developer Area
Bested the Acursed Foreman
Rescued the Diesel-Punk combat drone
Rescued a loose soul, cursed to wait in the dirt for all eternity
Rescued the fabled Shrinking Shotgun Surgeon
Rescued the squad Judas
Rescued the squad designated Blood Sucker
Defeat Satan in under 25 Minutes
Defeat Satan in under 35 Minutes
Defeat Satan in under 45 Minutes
Bested the writhing Wurm of the deep