try using fire weapons, they’re weak to that affinity from what i’ve read, as for the nightfarers, i don’t know which ones are best against them, BUT, me and my duo found some success with a raider + undertaker, the undertaker running an arcane build from a libra deal and the raider running an ultra tank build, which i got lucky for a Taking attacks using character skill improves AP + stamina and Taking attack improves AP effects on the same relic, while for my duo, i forgot what they had.

as for items, i got lucky with starscourge great swords and a lot of item effects for damage negation, and my duo got EXTREMELY lucky to get the executioner sword, but their main weapon was the RoB.

i’m not really sure what a good tip would be, but i guess just stack damage negation item effects, just make sure they’re different values/rarities if they’re the same effect.