The Howler

As of 5e Howlers are the only monsters native to pandemonium and is the only one to have appeared more than once throughout D&Ds history. Howlers are large fiendish pack hounds who feed on fear itself and whose howl drives those who hear it mad. Other than those base facts, Howlers have varied greatly throughout their appearances. All but the 5e version sport quills as a major feature, with the newest edition almost getting rid of the quills all together. Every edition has given the titular howl a different effect; 2nd edition mimicked the effects of pandemoniums winds, 3rd reduced Wisdom scores, 4th deals psychic damage and grants advantage, and 5th both frightens and incapacitates the target. The relative strength of the Howler has also changed from a relatively low level creature, to a CR 8 creature that hunts in packs of 2-20.

When researching both the Howler and cryptids, I found some similarities between the Howler and the Ozark Howler. Both of these creatures are large territorial hunters that posses fearful howls. At its heart, the Howler is a pack beast that you hear long before you see it coming, a creature that stalks and haunts you in order to feed of your fear itself. A fiend with glowing red eyes that contains features of dogs, cats, goats, and porcupines. 

As it already has a 5e stat block, I don't necessarily need to rework the Howler, but I want to. I feel that the quills were a core aspect of the creature, and a lower CR creature can be used in a wider range of campaigns (especially when appearing in packs). I have created two stat blocks; the first is a low level younger version, and the second is a larger version that demons and other fiends could ride as mounts.

Howler

D&D Monster Manual 3 4th edition