Lots of monsters have fear effects to terrorize PCs. What makes the peryton awesome is that its shadow mark will terrify the players. The first time you say, “So…as it passes over you, the beast’s shadow transforms to match…yours,” should be a chair-ruining moment for your players.
Of course, even without the shadow mark, a half-stag/half-eagle creature that eats hearts is plenty scary enough.
Also, in myth (sorta, see below) perytons originally come from Atlantis. So in your campaign, they might have a link to Azlant or some other sunken land. And since they speak Common, they may even have oral histories or valuable information about these places…provided you can cajole one into speaking with you. A few fresh hearts should do the trick.
Adventurers find themselves surrounded by dire wolves when a shadow passes overhead. Suddenly the wolves vanish into the forest, but the party’s relief is short-lived as a pair of perytons stoops to attack.
Polar perytons are larger than their southern cousins…and even more deadly, as they fly on the silent wings of snowy owls. The strange energies of the arctic affect them in other ways, too. A victim slaughtered and mutilated by such a creature has a higher than likely chance of rising as a zombie, wight, or even the dreaded wendigo due to the trauma and isolation of the death.
An archipelago is famous for being a nesting site for perytons, despite the fact that the beasts’ hunting grounds lie far to the east. Investigation reveals that the archipelago is actually all that is left of the mountain ranges of Denevair, the Sunken Continent—the perytons’ ancestral home. Interestingly, these islands lie a good hundred leagues north of scholars’ estimations for Denevair, which means they are likely filled with tombs and treasures as yet unexplored.
—Pathfinder Bestiary 2 207
Fun fact: the peryton isn’t mythological at all. It just feels like it. You go, Jorge Luis Borges!
Also, I’m in Boston for the weekend. Specifically, Dorchester. My friends have accents so thick you couldn’t cut them with cold iron. I should have typed this without any Rs.