Maybe Plagued and Astral Anchor are enough to tip a poison Necromancer to the "strong" side.
Before, I was trying to build around Poison Gas Cloud and other DoT effects but still felt I needed to have a swarm of undead critters to keep me safe, and I couldn't seem to afford both. But if you based your Necromancer around Malacoda yelling "come to daddy!" with Astral Anchor and Eagleclaw Boots keeping your Necromancer and Malacoda stationary (for the most part), most melee creatures and mages are going to have trouble dealing with stacked DoT from Malacoda, Idol of Pestilence, Plagued, Ghoul Rot, Magebane, Chains of Agony, Poison Gas Cloud and your Necromancer's Plague Master ability triggered by something that deals tokens with the poison attribute - which could be anything from Drain Soul to Venomous/Plague Zombie to Grey Wraith to Ichthellid Larva. Then you just have to worry about other Necromancers (!) and mages/creatures that can kill you from afar (e.g. Wizards, Adramelech Warlock, Johktari Beastmaster, Druid, maybe Warlords and Priest(esse)s that make heavy use of archers/snipers).