if you're niffing, bathory helps a little bit and it's help can be augmented by also using a deviling muffler... under normal situations, if you use deviling, the dullahan's will hit you with their shadow property attack (which happens quite often... sadly) for 1.8-2k... that's quite a big hit...
but if you're also using bathory, that attack will always miss. it doesn't, however, block ALL of the dullahan's attacks.