The apocalyptic forces of the Roaring, a KillTeam created to spread the dark fountains and plunge new worlds into neverending night.

faction rule in composition

dark fountains and the roaring in this context are probably a force of chaos, like a tear in space allowing the warp to spill into reality. As for which chaos god this would represent... idk brah i just wanted to mix my two current favorite medias, deltarune and 40k.