These are not extremely dangerous, but have the extremely annoying ability to corrupt your magical gear, giving it a -1 in a random stat. They have very low health, and a warrior will usually quickly gain the ability to kill them in one hit. From what I've seen they never counterattack or dodge, so make sure you get them to the point where you can one-hit them in melee, or kill them outright from range.
Never let them swing at you, they do not need to hit you to corrupt gear. Prioritize them over everything else and, if you can consume corpses in some way, consume magic golem corpses first so that witchys don't raise them.