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