[Mossy Toes]

If you want some mastery levels without sacrificing your Nurglord/Plague Marines, I'd go with 2 MLs on the SlHerald. Yeah, you won't get the benefit of her levels the first turn or two, but she should give you a needed psy boost (and might roll something fun like Shrouding or Invisibility).

If not, you definitely want a spell familiar on that Sorc. I'd also swap Sigil of Corruption for Termi Armor, which both cost the same on the sorc (thanks to not having to buy a force weapon): all in all, -1 invuln for +1 armor is a well worth it trade, I think.

Other than that, looks like a pretty damn crisp non-competitive list. Nothing too extraordinary, but nothing bad, either--looks fun!

 

[Mossy Toes]

about termin armour: he would not be able to run, though...oh, well...

He'd be able to run. Termi Armor gives Relentless, not Slow & Purposeful. He wouldn't be able to Sweeping Advance, sure...

 

[Mossy Toes]

That gets you fearless, albeit with the tax of a hellbrute and additional unit of cultists.

Also the minor cost of not having any Troops choices towards your battle-forged primary detachment, when the units you're fielding would normally fill that gap nicely for the same amount of points. Ah well, easy enough to work around.