I would like to bring SCP-1993 up as a suggestion.
http://www.scp-wiki.net/scp-1993
SCP-1993 "Your leg" could be found in it's room in an open safe, which was opened on accident by the researchers in the control room before the room in which it is located when the evacuation message was being told on the onsite radio system.
That may sound a bit empty, "Why would they accidentally open the safe door which is voice locked, when the evacuation was started?"
In the room where the researchers were there could be a voice recording voice used to vocally document tests with Class D subjects and 1993, you could pick it up and play the recording to learn that SCP-106 started to appear out of the floor in the room, and the researchers panicked, banging on the door to the hallway while trying to get it open.
They would on accident say the message that opened the safe with SCP-1993 in it
When you then enter the room 1993 and it's safe is in, you will see for example a dead Class D sitting against the wall with his right leg missing, replaced with a bare naked right leg instead which isn't attached to his body except for a couple of strings of tape or thread, sitting in a puddle of blood he had lost during the act of trying to remove his leg and attach 1993 to himself. At this point the safe with the new SCP-1993 leg isn't visible, but if you walk a few steps forward and look to the left, our Class D character would see SCP-1993 and would try too to replace his right leg with SCP-1993.
The leg wouldn't function as a leg anymore and from now on the Class D would walk around limping and dripping blood behind him. A med kit could be used to temporarily stop the bleeding but not the limping, and you would eventually die from blood loss, like if you were shot a few times by the helicopters and MTF at the moment in the game, or from an SCP attack;
with 096 being a 100% death if you saw his face,
and 106 being a 100% guaranteed trip to the pocket dimension if you weren't close to a tesla gate you could shock him with,
and 173 catching up to you every time you blink,
and the MTF being able to quickly hunt you down and shoot you, but still possible for you to hide from them in the office areas.
Short said, adding SCP-1993 would add an optional method to add more horror and scare to the game if you know about the SCP and it's properties, and a way for new-comers to get acquainted with the SCP and perhaps giving them a reason to learn more about the SCP Foundation.
Would like to hear your thoughts about this suggestion, especially yours Regalis.
What fun is there in making sense?
Now, if you will excuse me i have some chaos to wreak.
Resident forum robot monkey, and chaos incarnate.