There is no doubt in my mind that the Order of Mathos has members of the Endless Court in its numbers. We need to find out who they might be.
Perdeen was a town that once flourished in this moor, and members of its own community sacrificed it to the rifts. It is possible we might be able to find a link to members of the Endless Court inside of its ruins.
All that remains of Perdeen is spit out of the occasional rift. You'll have to search the rifts for its remains and the evidence we are looking for.
Maculav, Murovic, Newkosa... Hmm. Seek out any living relations of these three in Stillmoor, and interrogate them for any possible links.