Hey all. I tried my hand at creating an undead Challenge 30 monster called The Lingering Havoc which is a collection of body parts. Take a look and please let me know what you think. I'm open to suggestions and feedback! http://worldbuilderblog.me/2014/10/02/the-lingering-havoc/
Have you looked thorugh my monster maths articles?
If so I'll have a look. If not well... Tell me when you have 
OK my critique...
Lingering Havoc
- Average ability is a bit low (18.8 rather than 25)
- Max ability is fine
- HP are pretty high
- Regeneration and Absorb The Dead make HP even higher (@756)
- Damage is super high. This thing would simply opt for multiattack with 237.25 damage every round (1x death ray=109.25, 4x slam=128). By comparison Poison Breathe is meh. And I have left out the wights...
- Legendary actions not included in assessment, of course, since Legendary Creature is just a template. But the way you have applied it looks appropriate to me.
- It does looks OP to me. Ready for a TPK???