D&D 5E Stradh Von Zarovich, formidable Necromancer? / Necromancer build for 5e

[FormerlyHemlock]

This varies for players and monsters. NPCs don't really need to follow "the rules" and can have all kinds of unique or amped up necromancer abilities. Plus, since they're only around for 2-5 rounds of combat, full PC abilities can just make monsters too complicated.

Ack! I can't imagine having NPCs who only exist for 2-5 rounds of combat. At the very least I'd expect them to exist for several hours beforehand, possibly a few minutes of talking, then maybe 2-5 rounds of combat, and possibly days or months offscreen after combat.

I don't always stat out all of an NPC's abilities (I may assign four or five combat spells/skills and leave the rest as Schrodinger Skills) but it's important to me to know generally what they are capable of, and class + level generally provides enough of a framework to make that work. "Diviner 9" says a lot.

 

[Dkase]

There are stats for Strahd through out his various incarnations all over the place, with the most recent being 4E's open grave. For 5e you'd probably be best served by using the spell caster vampire template, though perhaps upping the level to your desired CR. As for other famous necromancer's in D&D, there was Azalin from Ravenloft. He and Strahd even have somewhat of a history as they are both Dark Lords of Ravenloft.
For unique undead, you'd be hard pressed to find someone better than Kyuss from the Age of Worms adventure path. All of the variants of the Spawn of Kyuss were quite memorable in a terrifying way when I played through it.