Any benefit to bringing other death units into a night haunts army

[hammer49]

Is there any benefit from bringing other units into a night haunts army from the other death armies ?

If so what are the units best to do so with and how ?

[hammer49]

I ask because my Partner is thinking of starting the army and likes various models through the death range, and I don’t have much experience with the death armies.

 

Any help would be most appreciated.

[That Guy]

Well, Nighthaunt works best on its own. Currently they really need a tome update to be considered competitive. 
There is an argument to be made about just spamming hordes upon hordes of bladegheist with some harridans and Hexwraiths under Emerald Host, have reikenor as a beatstick and reliable caster, have Olynder and a Cruciator and just create this crazy 100+ wound ethereal save army with multiple models getting revives and 5+ wards through the Cruciator, while you bodyguard Olynder with Hexwraiths. 

As for units to add to the army. On 2K you could consider a few options. This army lacks big monster units. There is the forgeworld Mournghul... but that's also a nighthaunt unit.
You can consider Nagash, since now you'll have access to him and he'll be a great asset. Just know that currently there's discussion if Nagash can benefit from the Emerald Host bodyguard ability, since he can't be a Nighthaunt unit himself, but he can be a general. Another option you have is Big Drogg Fort-Kicka, which is a Gatebreaker Mega-Gargant who can be taken as a Mercenary in death armies: 

Big Drogg Fort-kicka – Gatebreaker Mercenary If you pick this Mega-Gargant mercenary to be hired by your army, you must include 1 GATEBREAKER MEGA-GARGANT in your army as a MERCENARY unit. GATEBREAKER MEGA-GARGANTS can only be taken as MERCENARY units by Death and Destruction armies. 

Hope this helps a bit. There's also people who like Mannfred Mortarch of the Night in there.

Edited January 31, 2022 by That Guy