Almost rivaling the destructive power of the Harlequeen, the Cacchinnox is aberrant even by Joker standards; no less playful and anarchic, but crueler, more bloodthirsty. Whether friend or foe, its every action carries some element of malice, its sense of humor more focused on inflicting as much physical harm and emotional torture as it possibly can. Prone to bullying even their own kind, the beasts are are often kept deeply imprisoned within the Joker Hive.
A Cacchinnox blows thousands of colorful, toxic mucus bubbles to quickly disorient its victims. Its intensely shrill giggle is finely tuned to cause intense physical discomfort in most other beings, and a single focused squeak can inflict debilitating agony. Its rubbery body can compress to less than a tenth its length at rest, allowing the creature to launch itself like a spring.
Genetic sequencing places the Cacchinnox surprisingly far from other known Jokers, possibly representing an assimilated natural species or a relic of the most ancient, prototypical Joker lineage.
I've already got kind of a running gag now where the meanest and most vile monster in any given class is usually a dolphin, and I figure it suits Jokers most of all.
I'm not sure there could ever be a dolphin-like devil bird or arthropoid, but time will tell...