Tormented demons right now CAN be killed but are not worth the struggle. These are a couple suggestions to make them a little more possible to kill..
-The effect from being hit by a darklight needs to be extended, it doesn't seem that they are weakened for a long enough time period when you damage them with the darklight. (This needs fixed for sure)
-Being a multi combat zone it is very hard to fight just one at a time, there is always a second or third one coming at you and when their magic splashes, it is very difficult to keep your health up. I think the area needs to be made 1v1
Either one of these suggestions could make them a better boss to fight.. but the combination of both of them would make them a lot more fun to kill and try to get claws from.
