A Chaos Spawn is the wretched end-state of a mortal who has been utterly consumed by the corrupting gifts of the Dark Gods. Where a favoured champion might ascend to daemonhood, those who reach too far, fail their patrons, or simply attract too much unwanted attention are instead collapsed into a formless, ever-mutating horror.
The transformation is a grim mockery of reward. Blessings that once granted strength run wild until the body can no longer contain them, sprouting extra limbs, mouths, eyes, and tentacles in a churning riot of flesh. Whatever mind the victim once possessed is drowned in agony and madness, leaving only a mindless thing driven by pain and hunger. The Mark of Chaos that once signified favour becomes the seed of this final dissolution.
Among the Chaos Space Marines, the threat of spawndom hangs over every warrior who courts the gods' attention, a reminder that Chaos gives and takes without mercy. Warbands sometimes herd their spawn into battle as expendable shock-beasts, unleashing them to tear into enemy lines before turning on anything that moves. To become a Chaos Spawn is the fate the servants of the Chaos Gods fear most, for it is damnation without even the dignity of purpose.