Here is the full list of all 41 SCP: Containment Breach Multiplayer achievements.
Used SCP-420.
Obtained a liquid from the Coffee Machine.
Encountered the Possessive Mask.
Encountered the Zombie Plague.
Encountered the Sleep Entities.
Encountered the Shy Guy.
Found a Blue Key.
Encountered the Bad Composition.
Found the cure.
Lured the Old Man through a Tesla gate.
Encountered the Shadow Lamps.
Wore a GP-5 Gas Mask.
Encountered the Old Man.
Encountered the Builder Bear.
Acquired the S-NAV Navigator Ultimate.
Encountered the Creatures with Many Voices.
Encountered the Clockworks Machine.
Encountered a Recursive Room.
Encountered the Peripheral Jumper.
First played the multiplayer.
Recontained SCP-055.
Encountered the Old AI.
Acquired the "Telekill Alloy".
Found and equipped the "Lovecraftian Locket".
Swallowed a sample of Panacea.
Encountered an Old Cowbell.
Found a Jaded Ring.
Encountered the Ghost.
Encountered an Old Coffin.
Read the Encyclopedia of Common Diseases.
Encountered the Atrocity Skull.
Entered Doctor Maynard's office.
Entered Doctor Harp's office.
Acquired an Omni-level Keycard.
Didn't use console commands.
Escaped the Old Man's Pocket Dimension.
Encountered the Hole In The Wall.
Beat the game on Keter difficulty.
Escaped the facility in breach mode.
Became MTF in breach mode.
Became scientist in breach mode.