Beheaded are creatures rich in folkloric significance, whose origins—naaaw, I’m just messing with you. They're flying undead heads. Let’s not overthink this.
(Somewhere someone is already typing that I can't forget the medusa heads from Castlevania or the delightfully gross bouncing Kashira from Spirited Away. But it’s too late! Bring on the floating zombie heads!)
Enchanters and enchantresses rarely demonstrate proficiency in necromancy. (More hidebound magical colleges even require enchanters to select it as an opposition school, to better conform to the classical theory about such matters.) A notable exception seems to be Annisette of the Greensward, who is notorious both for keeping the head of her first husband as a beheaded familiar and for being so skilled in persuasion that her current husband never seems to mind. Speaking of said husband, this year’s model is Drake Haverton, who is rumored to encourage gem smugglers to use his lands and who has made enemies of at least two tribes of the scorpionfolk known as girtablilus.
Villagers near Redwing Bog never knock on doors; instead they ring crude triangles and call respectfully from the front porch. This is because Redwing folk are raised from birth to expect that any knock on the door may be a beheaded battering itself against the wood. Over the centuries the region’s redcap has stricken hundreds of heads off the shoulders of travelers, and occasionally the foul waters of the swamp spit one of them out as a beheaded—often the screaming variety—to roam and spread terror at will.
Notable beheaded found in Ylani include flaming beheaded that haunt the river docks every Fire Lantern Eve, the skull swarms given life by the slow corruption of the Tunnel of Bone, and the belching beheaded in foolscaps that guard the (surprisingly well-stocked) treasure vaults of the Laughing God’s temple.
—Pathfinder Adventure Path #43 82–83 & Pathfinder Bestiary 4 17
Beheaded fans will want to check out Pathfinder Adventure Path #43: The Haunting of Harrowstone, which introduced the beheaded and served up giant and medusa variants as well. Speaking of medusa heads, here’s a pretty wonderful appreciation of the cleverness of Castlevania’s flying menaces.
The “classical theory” of magic mentioned above is of course from 2e AD&D, which prohibited enchanters from using evocation and necromancy.
Somewhere I have a copy of Severance by Robert Olen Butler, a book of short stories all told from the point of view of a decapitated head (each only 240 words long, for obvious reasons). I’ve never been able to bring myself to read it.