Dark Berserkers are Animals. Likely this monster is called a Berserker, and "Dark" is a subtype applied to Berserkers and a variety of other related evil human monsters.
Berserkers are large men who serve as the muscle of their evil, demon-worshiping cult. They are massive, powerful men who wear hoods and loincloths and carry massive mauls, with which they are happy to bash your brains in. Berserkers have a special overhead smashing attack, which they telegraph by powering up their mauls with a reddish glow. Their overhead attack is highly damaging, but if you dodge it the Berserker will hit the ground so hard their maul breaks through the ground and gets stuck there. While the Berserker struggles to pull his weapon free, he is defenseless and can be killed shiftly.