Brown chaos serpent
From DoomWiki.org
The Brown Chaos Serpent is an enemy from Hexen. They are identical to the Green Chaos Serpent, but their skin color is brown, instead of green. Brown Chaos Serpents spit green fireballs which do either more or the same amount of damage as the Green Chaos Serpents fireballs do. A player hit by a green fireball is not poisoned. They have 250 Hit Points.
Brown Chaos Serpents first appear in the Seven Portals' secret level: Bright Crucible.