Here is the full list of all 12 Sam & Max Save the World achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Completed episode 6.
Cut off Hugh Bliss' head.
Used the shaving cream on Bessy.
Completed episode 5.
Found a “bug” in Sybil’s VR.
Completed episode 4.
Found the easter egg at the White House.
Completed episode 3.
Got a score of 21 or more on Whack Da Ratz.
Completed episode 2.
Completed episode 1.
Got Whizzer to sing the Soda Poppers song.