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