Looking at an all Ringwraith on Fell Beast army at 800 points.

So far looks like this:

Khamul the Easterling on Fell Beast
The Knight of Umbar on Fell Beast
The Undying on Fell Beast
Shadowlord on Fell Beast
Ringwraith on Fell Beast 1/7/2

So got 2 combat wraiths and 2 casters along with a budget objective grabber. 3 of the wraiths can regain or don't lose will so can stick around long term.

I like the Dark Marshal for his static F6, good casting and cool name and think under the new rules the Dwimmerlaik has got a boost but think the shadowlord may come in handy over these 2.

Or I go 3 named wraiths and 2 un-named and spread the MWF points evenly over 2 instead of having 4 named and 1 weak wraith.

Thoughts?

I would take the dwimmerlaik if you can find a way to fit him in, the 4+ roll to make a hero use 2 will rather than one to resist your spells is unbelievably powerful, your magic will be almost unstoppable and your opponent will be put under a load of pressure to resist at the right times as any time they do so they run the risk of losing all/most of their hero's will. The Undying is great as he'll regenerate his will loads due to the other spellcasters and he's a great leader. Shadowlord is nice as you'll get shot a lot, but is not necessary against every army. If I were you I would take the Undying, KofU, Dwimmerlaik, Shadowlord and the unnamed wraith, as KofU does the combat role better than Khamul IMHO and he has more might and better casting values, and you need your wraiths getting their spells of every turn.

I would probably opt for 750p game (unless 800 is necessary). And take:

*Witch King, fell beast, morgul blade
*Knight of umbar, horned fellbeast
*Dwimmerlake, fellbeast
*Shadowlord, fellbeast

Overall: 745p and full witch-king.

I would not take khamul just because... He perhaps stays a little longer alive in optimal situation than some other fellbeast, but if he gets surrounded he won't fight any better than others basically. Khamul has worst spell-ability in game too. Undying could be wiser solution instead khamul if u want a long-surviving hero. Not like that, the khamul looks the best ringwraith to my eye and that way i adore it (won't affect to fellbeast though).

Thanks. It is for 800 so an extra wraith over equipment seemed the better option.

The Dwimmerlaiks abilities would really put pressure on enemy heroes so that would be handy. Though my own might store goes down.
I think if I went with the dwimmerlaik I would swap out the shadowlord. Although Khamul is a worse caster I cant help but think in protracted games being able to regain will would be handy and I do have a lot of magic already. Plus F6 means i don't have to always rely on transfix or heoric strikes. But shadowlord would be essential in some games. There's some tough decisions to be made.

Alright, in this case I agree with many fellbeast... Let's say:

6 nazgul on fellbeast with 10w 1m 2f (drop one fate from one nazgul) would be mass... But it wouldnt stay too long around... I would prefer:

-Witch king 2m/14w/2f, fellbeast
-Dwimmerlake, fellbeast
-Your Favourite Named, fellbeast
-Nazgul 2m/12w/2f, fellbeast
-Nazgul 2m/12w/2f, fellbeast

Overall: 800p, 5 units, 8might. U can destroy enemy wizard staff, and even mightiest heros fall against dwimmerlake. Shadowlord could be good choice for second ringwraith, if u just keep forces first in formation until u are close enough to archers/other troops. Or then Khamul or any named u like! Even Darkmarshal would not be bad choice, since extra roll on enemy's priority can save the day... Anyways...

So been thinking maybe the dwimmerlaik would be handy to make opposing heroes burn through their MWF, but what to drop?

A lot of people are saying the shadowlord, but I'm still clinging to him as the chance of crossbows etc having a good round of shooting and tacking out a fellbeast worries me. But he seems the better option to drop than the combat wraiths who will do the heavy lifting.