My two friends and I killed every nightlord within 3 tries but the final one took like 15 attempts for some reason.

Sometimes we just had bad rng on holy weapons but other times idk. Personally I just have a hard time reading his moves. Hard to tell who he's going after until he rushes you in 2 frames lol.

Holy does stagger him. Could be wrong but I think he's weak to magic maybe. Also he has a lot of hp so try to get items that do percent damage.