Here is the full list of all 37 Shadows Over Loathing achievements.
You learned all nine Shadow skills
You destroyed Gobulon Prime
You executed a perfect heist
You received the hobo camp's highest honor
You found a fancy necklace
You tuned a radio with your talented talons
You posed for two different fedora pictures
You filled the gas can up ALL the way
You closed the Time Loop
You defeated the Ziggurat Goliath
You saved the village of Sandwich
You ate a stuffed pepper
You bought a barrel
You got locked out of the universe because of a temporal paradox
You completed all of Don T's assignments
You beat Jessica at chess
You got into the Secureberus vault
You maximized morale in the Maize Maze
You gave a tentacle ten tickles
You got a fully-decked out Monster Shack sash
You solved Mrs. Brewster's mystery
You won all the prizes at the Ocean City Boardwalk
You drove enemies out of 23 Hilbert House rooms
You made peace with the Fishmother
You passed all nine SIT courses (requires multiple playthroughs)
You met Largestmouth Luke
You helped the workers of Haim Quarry
Gabby saved the universe
Obie saved the universe
Molly saved the universe
Barker saved the universe
Adams saved the universe
Simone saved the universe
Alphonse saved the universe
You completed the game without fighting
You unlocked every cat
You flushed every toilet