Wintherin

The Wintherin are war beasts utilized by both Night Sentinels and Davoth's demon army.

Night Sentinel Wintherin
The Wintherin are huge beasts reminiscent of dragons in shape and appearance. However, it's unknown if they are legitimate dragons or members of an alien race that was domesticated for generations. Still, it can be accepted that these creatures are natives of Argent D'Nur, which is the same homeworld as their masters, the Night Sentinels. Sentinel Wintherin are shown to be white in color, have four horns, an angular head without visible eyes (which vaguely resembles a skull), and long serpentine necks. Overall, their anatomy matches the classic depiction of dragons with the position of their wings, which are located above the shoulders, and by having 4 pairs of limbs alongside a reptilian body structure. Near the chest are short but slender forelegs, which are possibly used in attacking targets directly. They have a purplish color fading on both their wings and upper abdomen. The left portion of this creature's tail is purple in color, with white stripes nearing the tip. They have a hook-like barb at the end of their tail used for an unknown purpose (possibly for melee combat). The last thing that can be said about this race of beasts is their ability to breathe out a stream of pale flames. These cold colors differentiate them from their counterparts faithful to Davoth and Hell. Such abilities represent them as a beast made and tamed for war.

These creatures are actually new to the main canon of the Doom Universe. Thus, any information that can be given is more speculative than confirmed. The closest thing that can be described as something more acceptable is the Wintherin originated from the same world as the Night Sentinels. Possibly, these creatures are a heavily-used mount with how the final battle is depicted in Doom Eternal - The Ancient Gods: Part 2. So, it can already be stated these are beasts who were always a preference for the Night Sentinels.

Demonic Wintherin
The Wintherin used by Davoth's army contrast greatly from the Sentinel variation. They are very similar to their namesakes, which are faithful to the Night Sentinels, in practically the shape of their body, head design, and even behavior. However, this variant possesses some notable differences: they are dark blue in color, have red instead of purple stripes, two glowing red horns, thin spikes along their back, and two barbs on the tail instead of one. As expected, like the Wintherin used by the Night Sentinels, they also spit out fire. The flames they produce are more intense, more reddish with demonic colors. These infernal beasts are usually seen near the capital of Hell, Immora.

As said before, this is more speculation than something confirmed. It could be assumed these Wintherin variants are the ones accompanying the Night Sentinels who allied themselves with Hell, alongside the purpose of the Khan Maykr.