If you're wondering why I don't use them it is because I don't typically like save or die effects. I know I'm writing old school stuff, but I've just never been a fan.
Krast, Mage of Kyuss
The half-undead wizard known as Krast wasn't always a loathsome creature. His early days were spent adventuring. His life was changed when he and his party encountered a forgotten shrine to the Worm God. Only he and the party's warrior, Castellen, survived the encounter. While Castellen retired from adventuring and tried to put the encounter behind him, Krast became obsessed with the curious green worms and their affects on the living. Through research from various forbidden tomes he has begun the long and arduous process of becoming a Worm the Walks.
Armor Class: 7
Hit Dice: 10
Move: 90' (30')
Attacks: Staff or Necrotic Ray
Damage: As Staff (plus special) or 1-4 (ranged)
Save As: Magic-User 10
Krast casts spells as a 10th level Magic-User. He usually has the following spells memorized: Magic Missile (X2), Sleep, Web, Detect Invisibility, Phantasmal Force, Necrotic Bolt (X3, treat as lightning bolt, but damage is negative energy instead of electricity), Dimension Door, Polymorph Other, Wall of Ice, Animate Dead, Cloudkill
While technically living, Krast has many traits similiar to undead. He is immune to sleep, charm, and hold spells. He cannot be turned.
Any living creature hit by Krast's vile staff must make a Saving Throw vs Death Ray/Poison or die and become a Spawn of Kyuss.