Spirits of air don’t just inhabit mountain peaks and open plains. Mihstus are spirits of spoilt air, dank air, oxygen-less air—the stale stink of the long-sealed tomb. They are air that doesn’t want to be disturbed, that wants to be preserved in isolation, that is inimical to life.
Given their deadly embrace special ability, they might even be the spirits of explosive decompression—you can imagine a spelljamming/voidsailing campaign where spacewalking PCs have to wear special suits to shield them from the attention of the void’s jealous mihstus, who loathe all air breathers and thirst for their fluids.
Also interesting is their choice in companions—the Bestiary 2 mentions rakshasas and cloud giants. This points to a sympathy with diverse other selfish and evil creatures who enjoy hunting, blood sports, and otherwise spreading misery.
A room in a tomb complex contains a sealed door, a small stream, and a very well hidden cache of potions of water breathing. If the door is opened, stale crypt air spills out, fouling the room and bearing with it a mihstu enraged at being disturbed. Alternately, if adventurers use the potions to bypass the next room entirely by remaining underwater, the mihstu never senses their presence.
On the trail of a mass murderer and vivisectionist, an adventuring party raids one of his safe houses, a magically refrigerated room in a slaughterhouse decorated with corpses of his latest victims. One of the criminal’s summoned accomplices, a mihstu, is still in the room, kept stunned and senseless by the cold. But the party’s investigation warms the room enough to rouse the elemental creature, causing the splattered gore on the floor to rise up into a tornado of blood and claws.
A powerful fey has come to power in the Endwood, calling herself as the Handmaid of Air and Darkness. If she is not an actual servant of the famous Queen, she is at least a canny player, invoking the Queen’s power without presuming too much. But perhaps she does represent the dread faerie monarch…for her constant companions are personifications of Air and Darkness themselves, in the form of a mihstu and a soul eater.
—Pathfinder Bestiary 2 190
I should have mentioned this before now, but Penny Arcade combined D&D and the holidays in one neat package. Enjoy it starting here. And happy holidays!