It's literally just Battle Royale for SCP: Secret Laboratory.
REQUIRED for v1.1.1 and earlier: https://github.com/ShingekiNoRex/SCPSL-Gamemode-Manager
You will spawn as a Class-D in a random room around the facility.
When MTF/CI spawn (it is always changed to CI), thier job is to kill the Class-D Personnel.
The round will end when one Class-D is left, and the winner is announced in the command console.