The flying demon (called the harpy demon by some fans) is a new monster introduced in Doom Eternal. Little of it was seen in the QuakeCon gameplay footage, but what is known is that it can flutter in the air or land, possibly for terrestrial combat, though this has yet to be confirmed. They appear as small, frail humanoids with bat-like wings, strongly resembling grotesques or gargoyles in nature.
A flying demon called the "imp" was originally detailed in the Doom Bible by Tom Hall during Doom's initial development, before the name of imp was reassigned to what was then known as the "demon trooper." It is presently unconfirmed whether or not this detail has had an influence on this new monster design.