I think the jetbike farseer was the best idea so far and shows where the discussion should head. You need something that can deal with it at range because in cc, the nightbringer is better than any other model.
One interesting option would be a carnifex with two venom cannons, regenerate, +1T, +1W, +1BS. Have him stay away as long as possible and he should be able to put through about one wound per round of shooting. By the time the Nightbringer gets close enough, the carni should be able to finish him in cc. If you want to have an even better chance give the carni some cc upgrades as well.
A hive tyrant with venom cannons and all the stuff needed to shoot better would do well also, but without the regeneration, will be more susceptible to the nightbringer's return fire. On the other hand, its wings would allow it to stay play keep away really well. The fex should be able to put through a little more than 1 wound a turn, and could stay out of range for a couple rounds of shooting at least. The 6+ invulnerable save would help a bit against the return shooting as well.