They can work well complimenting a defensive build with your lord- 5 pariahs, lord W/ veil of darkness and nightmare shroud, sadly no solar pulse, but some things have to go if you want them in your list.
In this case five work better then ten and my only job is to make sure one of them lives. Forget about trying to assault with their warscythes and forget about shooting. If I’m shooting at you, you can shoot at me, and five of these guys are easy to break- let your immortals deal with the 24” range shots.
Fighting Necrons is all about breaking their core, getting in there, assaulting, close shooting and phasing them out. Every player knows this, and this is the very thing I’m counting on and want to turn against my opponent. They will be getting close to my core, and my job is to keep them away for as long as I can so I can shoot them to death.
When I set up I’m going to look for a place where I can completely block LOS to my pariahs if it exists on the talbe- a bunker, corner wall, etc. If I can’t completely hide them then I use the monolith as mobile terrain. IF I can’t do that then they are hidden in the back out of range and move up turn 2-3 so they are in the front when my opponent hits my ranks.
The P’s job is just to project that LD 7 bubble as long as they can just out in front of my army. When my opponent enters that bubble I start using the Deceiver’s morale power and popping off nightmare shroud like crazy. If this pushes my opponent back it buys me more time, if it doesn’t then they have to shift something over to taking out the lord and pariahs since nobody wants to take forced LD tests for the next few turns. The idea here is to push them back with failed morale or force them to shift priorities for a turn- either way it buys your core some more time.
Now why VOD on the lord and not a destroyer body? Well, in this role the lord is going to be hanging back with the pariahs and the core of your army. As a last resort I also want him to be able to zip in and contest objectives at the last turn. Normally I do this with a destroyer body, but since I am hanging back I won’t be able to reach far objectives- the ones I want to contest in time. VOD gives me that long shot deepstrike shot of landing and contesting, so that is why I’m working that in there. If you have a lot of scarabs and destroyers in your list to contest, then by all means drop VOD and go with solar pulse and a few other toys. Pulse could also work really well with this build by attaching your lord to the Pariahs and popping it off to buy them another turn of protection…