I knew very little about the mothman when I first heard of it. Fortunately, Mystery Monsters Revisited just came out. And now I know so much more very little!
That’s not a dig at contributor Anthony Pryor. He’s writing about a monster whose entire point is inscrutability, and he did a nice job with the leeway he had (plus he offered alternate abilities, cursed items, and plot hooks to boot). Unlike, say, when Dragon Magazine pulled back the curtain on mind flayers (“Wait, they’re from the future and went back in time to prepare our world so that they can exist whaaaa—?”), it’s too early to reveal that much about mothmen—doing so will only pin them down. (Heh. See what I did there?)
So yeah, the mothman has some hurdles: 1) It’s a cryptid, and not a well-known one (dating only back to 1960s West Virginia, and without the Internet boost the chupacabra got); 2) it’s new to role-playing, and 3) it’s not supposed to be explicable. Oh right, and 4) most people don’t think moths are that scary, let alone mothmen, especially when the cultural antecedent is that one guy in Watchmen and Arthur from The Tick.
So I think the trick with the mothman is to hint at its presence (or at least its possibility) early. Have it come up in a tavern tale…and have those who don’t scoff at the teller be truly terrified. Build up the victim’s credibility with the PCs (and the players). So when the mothman finally appears, ideally the reaction at the table won’t be “A moth? I’m fighting…a moth?” but rather, “It’s real! Oh no!”
Mothmen are also excellent success/failure-nudgers. Did your party romp through the dungeon? Have a visitation from a mothman as a spoiler to throw them off track or deplete them of loot. And while parties that make bad decisions (“Leave the decapus in the jar alone!”) deserve what they get, some nights the dice can just crucify a table unfairly. Let the appearance of a mothman be a balm (“We were meant to fail.”) and a dash of adrenalin “”There’s more behind this than we thought!”).
And of course, there’s that nagging sense that mothmen aren’t just visitors from afar…they’re visitors from the far future…
An escort job becomes a race against bandits, humanoid ambushes, and especially accidents and vile weather. Eventually the adventurers realize that someone is stacking the deck against them; someone wants their charge (a golden-skinned merchant of something he calls “chrysanthemum rockets”) to perish. A mothman is responsible, and if it cannot achieve its ends through subtle means (especially nightmare and phantasmal killer) it will resort to black tentacles via its agent of fate power, and then attempt modify memory on any witnesses.
Delegates of the Elven Court visit the town of Robin Crest, long said to be haunted by a banshee. The pair of clerics is tasked with laying the evil revenant to rest. Their work reveals no banshee but a mothman. But is its interest in the town it continually curses, or were the decades of disasters all a ruse to lead these particular priests here…and why?
Mothmen don’t look so alien in spacefaring solar systems. Elven armadas have long used insectile ships and elf/insect half-breeds and hybrids as soldiers. Mothmen appear to be some kind of super-weapons gone wrong—scions of an experimental, perhaps even far-future development gone rogue and now operating of its own accord.
—Pathfinder #16 88–89 & Pathfinder Bestiary 2 194