Beasts of Nurgle are joy given a shape only Nurgle could love: sluglike bulks that gallop with puppyish glee, tentacles lolling, trailing slime that blisters stone. They adore the living. A Beast will chase fleeing soldiers across a battlefield purely to lick them, crush them affectionately, and prop them back up to keep the game going — growing sadder and more confused as its playmates keep breaking.
Their fate is the Cycle in miniature. A Beast disappointed too many times grows sullen, then bitter, and at last crawls away to pupate, hatching as a rot fly with all that bounding love curdled into venomous spite. The legions treat both halves of the creature's life as equally sacred, which says everything worth knowing about Nurgle's idea of love.