Fallen Angel

Fallen angels are powerful beings who've been cast out of their former celestial home after having turned from the ways of goodness to those of evil. They now make their home in the nether, but can be found lurking deep within the overworld as well.

In combat the angels will fly around quickly, unleashing balls of corrupted light in rapid-fire streams. While these don't do a lot of damage they ignore armor and force the player to move to being hit by the whole barrage. A fight with one is a classic boss-like extended dual.

Origin

The fallen angel was originally developed for a different mod that was discontinued. They are based on the dark bishops (also here) from the game Hexen: Beyond Heretic, but were renamed, re-themed, and toughened into more of a mini-boss. There actually was a monster called a fallen angel in Hexen II.