Older theory of mine, the denarians deny entry into reality of things that would mirror the 4 horsemen by taking up that metaphysical space.
Some slight evidence of this comes from Woj about Thomas's demon vs iirc(if that wasn't it, I sure can't remember what it was vs him doing/having..)taking up a coin. The demon would get the short end of the stick. Why? Because I think the mirror it exists in is exactly what the denarians utilize.
Used to have this whole theory that it's the walkers, and the walkers with an EG style beast of burden, a la human host would be Riders.
That theory... Is somewhat broken by the 3 interconnected walkers. Though I think the fourth one is still technically the blackstaff.. MWs Walker stick.
Looking purely at Nic in DMs though. He utilized a plague curse set by a timed schedule. Sacrificing someone with the metaphysical mass of a KotC. Created havoc and then blamed it on a non supernatural source, terrorists. Thus downplaying any supernatural beliefs that might have been envoked. At the least, he was dispersing the apocalyptic state of mind, so it wouldn't build up in one spot.
Although.. later connections between fearbringer manifesting and Molly, make me believe this was also the point in time that she firsted used magic. An that she is in fact, the primary manifestation he was attempting to co-op.