“A wight? How bad could it beEEEEEEAAAAAAGGGHHHPUTITOUTPUTITOUTPUTITOUT!!!”
—Every high-level adventurer ever
Any adventurer who mistakes a winterwight for a frost wight is in for a nasty surprise. This negative energy-infused undead is truly a next-level threat—understandable, given that previous versions have showed up in places like the 3.0 Epic Level Handbook or in the service of Acererak.
And the surprise factor isn’t a bad way to deploy a winterwight. They aren’t geniuses by any means (Int 11), so only the most exceptional examples would ever be the big bad guy at the end of the adventure. (That’s more a job for a lich or tzitzimitl.) But as spoilers and level bosses, they're outstanding—and scary. They're the thing you have to get through before you face the big bad guy…provided they don’t bang you up so bad you call it a night. Winterwights are tough enough (channel resistance, DR, SR, etc.) to soak up a party’s resources, and the first time a player finds her PC erupting with blightfire and burning through Con, the whole table is going to freak out…especially if they thought defeating that icy skeleton was just going to cost a channel attempt or two.
There is at least one city in Hell ruled by winterwights. Jealous of the infernal dukes’ control of balefire, a grasping count tried to harness the Negative Energy Plane for a weapon of his own. He was destroyed instantly and Hell itself encysted the city in ice to seal off the rupture. But the count’s lieutenants survived as winterwights, who rule over a now-frigid city of ice devils, wraiths, and rime-covered lemures.
Trapped on another world, a party of adventurers tries a desperate gambit to get home. Rather than planet-hop, they will plane-hop, sailing through the Deep Shadow. But unlike space, the umbral sea is not empty. Chunks of black ice—half-iceberg, half-asteroid—float in the blackness, and ghost ships crewed by hatewraiths board and slay at will.
There is a blizzard so powerful it exists in three times at once—during a mammoth migration from prehistory, a record-breaking medieval wolf winter (so named because of the winter wolves that rule the streets), and a far-future siege where rifle-bearing soldaty lay siege to a city of fascist tieflings and frost giants. In the whiteout conditions of the blizzard, the time streams mix and merge, with bands of soldiers as likely to stumble upon a pack of worgs, a smilodon, or a devil-possessed tank. The key to escaping the blizzard is to warm its heart—the icy heart of a winterwight no less.
—Pathfinder Bestiary 2 283