So our Class Masteries are terrible. After 2 months trying to make something that works with how strong DK, Sorc and Werewolf are, this is what I believe is the only way to make this playstyle work.
For this build, first of all, just to get it out of the way, it doesn't have Major Breach. Breathe in, it's ok. We have Minor Breach and a Penetration line in Rush of Agony. I'm not even using the Lover because even without Major Breach it's a small difference from the Shadow and I like to also have bigger heals.
I saw some players using Wretched Vitality and I think that's a terrible set with horrible opportunity cost and for NB in particular it's way overkill. The Stamina Recovery line on Rush of Agony + Khajiit + Recovery Food and no Vampire is more than enough sustain. You may want to adjust the Jewelry Glyphs if you're a different race. If you want even more Stamina sustain, you can switch Race Against Time for Phantasmal Escape, which also gives Major Evasion, something important if you're insane and want to brawl vs DKs.
I like the Disease Glyph since it's AoE but in theory a Double DoT poison is stronger.
It's very important to have Soul Harvest on the backbar as every instance of Critical Damage or Healing will give you 2 Ultimate from the Class Mastery and the high ultimate generation is basically what makes the build worth playing.
As for Healing Soul, in theory the Druid Script is a lot of sustain but in practice it doesn't do much. The healing is almost nothing but it gives more ultimate.
UESP: :EsoBuildEditor?id=689340