Dark Doctor Harold is a spirit in BLACKSOULS 2 that will invade you at a certain part of the Mental Ward area. Just like all other spirits, he’s kinda demented and will start going on about how you can’t meet a certain girl again, presumably a certain patient, even though she favors you too.
He can be tough to overcome so if you’re weak it’s definitely the best choice to just avoid him. There’s a certain phase in the fight where he gets more aggressive.
Killing him will give you a Dusk Crown Ring, and a Black Soul.
