The possessed murderer

This colleague is actually dead, intellect devoured by the blood parasite they freed in the R&D lab of level -13. Their face is twisted in a horrendous grin and their hands (or other appendages) are deformed into nasty claws. They are covered in blood, particularly around the mouth from the vitals of all the evening's victims. If needed, remind the players of their interaction with this colleague about level -13.

BLOOD PARASITE. HD 5 (27 hp), ARM –, ATT claws d8 (x2), SP mimicry, hide in a crowd, immune to magical attacks and mental effects, ML Δ10.

• Death and possession: If the parasite manages to bring a PC down to 0 hp and that character fails their CON roll, not only do they die, but the parasite takes possession of their body. Use the above stats with 14 hp. If the murderer falls down to 0 hp, the possessed body falls to the floor, broken, and a purple, shadowy mist emerges from the body. It hovers for a few seconds, then disappears through the floor. In its disincarnated form, the parasite is immune to most damage.
• Reinforcements: Every turn, one colleague shows up to help, armed with a broken bottle or a salad fork. Start with any PCs occupied elsewhere, then add an NPC of your choice per turn – no need for stats, just roll Δ4 damage to the murderer the first turn, stepping up the die for each new combatant. When the die steps down, describe an NPC getting killed or knocked out.