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 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.
Used the shaving cream on Bessy.
Found the easter egg at the White House.
Completed episode 4.
Found a “bug” in Sybil’s VR.
Completed episode 5.
Cut off Hugh Bliss' head.
Completed episode 6.