In the blurb of ToM it was already mentioned that Perrin "is now hunted by specters from his past: Whitecloaks, a slayer of wolves, and the responsibilities of leadership. All the while, an unseen foe is slowly pulling a noose tight around his neck. To prevail, he must seek answers in Tel’aran’rhiod and find a way — at long last —to master the wolf within him or lose himself to it forever."

Since Slayer is mentioned as a separate threat from the unseen foe in this text, it was speculated that the unseen foe might be Fain or Aran'gar. However, in the light of the prologue it's clear that those options are gone.

Others thought that the unseen foe might be Cyndane, Moghedien or even Demandred, though one wonders why a Forsaken would act such indirectly, namely "slowly pulling a noose around Perrin's neck" instead of simply balefireing Perrin (especially since Moridin just ordered that).

Who do you think the unseen foe might be and why does he apparently act rather indirectly? Was the unseen foe already heard laughing in Perrin's PoV in ToM, prologue? It seems to be related to TAR, if Perrin has to seek answers there to prevail against the unseen foe. Might Graendal be an option after she left Arad Doman? Or is it related to the creatures in TAR, which also killed the noble from Shara in TDR, ch.9?