SCP-5935-1 is referring to an entity who's the last son of IS, an entity talked about in SCP-4840 and SCP-6666. An Overseer, who lost his son Jacob, is influenced by his dreams to search for his son's name, in TABOO. While there, another, unknown entity sacrifices something to make sure the Overseer goes to the part of the forest where SCP-5935-1 is. The entity and the Overseer make a pact, and the Overseer gets Jacob back. However, it's actually the entity, pretending to be Jacob.
The Foundation quickly figures out what the Overseer did, and contain SCP-5935-1. The Overseer tries to release Jacob, but is reprimanded and put out of the Council by the other Overseers. The entity manages to breach Containment, and takes the Overseers wife, Elisa's, name, before being confronted by the Overseer. The Overseer agrees to give the entity his name, in exchange for getting some more time with entity, pretending to be Jacob and Elisa. SCP-5935-1 agrees.
The Overseer builds Pandaemonium, and they live normally there for a while, with clones made by SCP-2000. However, the entity grows suspicious, and figured out that the Overseer has tricked it, and trapped it in Pandaemonium, which is ever-expanding, due to the Architect being there. The entity promises to find a way out of the location, steal everyone's names, and come back here to stay with the Overseer, and leaves.
The SCP-Foundation quickly figures out the situation, and put the Overseer in a medically induced coma.
Note I am not sure, the file for this was extremely esoteric. I've tried the best I can, if you can provide an better description, you can put it here. Thanks.