I’m pretty sure I’ve waxed poetic in this space about my feelings—and even my feels—for the Creature Catalogue. It was the first “basic” D&D supplement I ever bought, before even the Expert Set, and I’m pretty sure I was still only in 5th or 6th grade at the time.
One of that book’s standout monsters was the soul eater. The name and the illustration alone would have been enough—baleful eyes and ghostly white claws erupting from a malevolent black cloud. But the soul eater was also memorable for the mystical connection it had with its summoner. If the soul eater was defeated in combat—or even if its target simply died of any cause before the soul eater could devour his or her soul—it would then go haring back to strike at the magic-user who called it at double (20!) Hit Dice.
Soul eaters made it into AD&D with the Mystara Monstrous Compendium Appendix and from thence to Pathfinder and Golarion. It no longer returns at double Hit Dice, but it’s still a nasty, Wisdom-draining piece of work that fits nicely among the soul-devouring daemons of Abaddon (or whatever bleak waste is appropriate to your campaign).
A party of adventurers has two enemies chasing after it. The first is a soul eater called into service by the disgraced prelate whose public downfall the sellswords recently caused. Trailing in the outsider’s wake is a human souleater (see Book of the Damned—Vol. 3: Horsemen of the Apocalypse), who wishes to witness the dread entity at work.
The Galloping Inn gallops across the world so frequently for a reason: The owner, Vernur Havershed, is fleeing a soul eater. Worse yet, he has only himself to blame, as he was the mage who originally summoned the outsider in an ill-starred scheme for revenge he now regrets. The persistent soul eater has followed Havershed across the world’s five continents more times than he can count. Even galloping to the Planes seems to throw the soul eater off the scent only temporarily…
Summoning and teleportation magic cannot pass the wards that border the microstate of Temblin. This fact, along with Temblin’s crack halberdiers and musketeers, allowed it to become the Lowlands’ banking powerhouse. But now Temblin is devoid of life. A soul eater escaped and gorged itself upon the tiny nation before the alarm could be raised, and now the bloated and powerful (Advanced) outsider prowls the warded perimeter endlessly looking for a way out.
—Pathfinder Bestiary 2 254