Here is the full list of all 12 Sam & Max: Beyond Time and Space achievements.
Completed episode 5.
Completed Sam & Max: Beyond Time and Space.
Won all upgrades for the DeSoto.
Witnessed Satan berating the staff each time hell efficiency dropped.
Completed episode 4.
Tried every dialog choice with all AI personalities.
Completed episode 3.
Tried every possible body part on the monster.
Offered the granite sandwich to everyone on the island.
Completed episode 2.
Completed episode 1.
Celebrated the bug's birthday before his family arrived.