Antibody

Every organism has its own defense mechanisms. Your heroes block blows with steel plate and end threats with shot, blade and light. Their foes respond with muscle and eldritch power. And there, in the heart of the World, the creature dwelling within (or is it the World itself?), the Antibodies face that task with clacking mouths and shots of phlegm infused with the Creature's magic, hurled in their deadly arc at your unfortunate foes. Making things worse is their tendency to associate with the flying polyps in the Darkest Dungeon's sprawling maze, which fire toxic bile at your heroes, not only blighting their victims but also coating them in pheromones, which signal to the Antibody to continue the assault with its stunning shot before a Flesh Hound devours them alive. In this way, the Heart of the World protects itself from direct assault and spares itself having to fight the courage-maddened fools that enter its demesne.

Behavior
The grand Organism beneath the manor is, if it has a virtue at all, smart, smart enough to forgo the wasted energy and resources it would take to equip the Antibodies with a proper brain. On one hand, that means its spittle is aimed fairly randomly, although they have twice the chance to shoot at a marked target, and it doesn't have any other methods of attacking. On the other, having no mind means having no real weak spot, and though it may look like rubbery flesh, its simple structure and infusion of nameless energy means it's not only hard to put down but also challenging to stun, and not particularly vulnerable to bleed effects, though blight works suitably well. It is only found alongside Flesh Hounds and Polyps; Flesh Hounds go down a bit quicker, but don't have the damage or reliable stun of an Antibody, whereas Polyps die quick, with 13 fewer HP and lower resistances than Antibodies. Plus, Polyps deliver the mark with their blight attack that makes Hounds and Antibodies lethal; kill them first, then focus down the Antibodies unless you've got Hounds targeting a marked low-HP hero.