undead pet query

[CryptbornAkryea]

I've never understood how one acquires an undead pet. The math portion.

The example I'm using to learn with is a lvl 8 dread necromancer with a rod of undead mastery. Assume he managed to get desecrate cast before the creation of his pet.

How many hd am I limited to?
Heck, what would be some entertaining choices for such pets?

edit: clarified my questions

[The Viscount]

At level 8 you can control 2*(4+Cha) undead per class level, so 64 + 16*Cha HD of undead. Assuming you are using animate dead, you can only create 32 HD of undead per each casting, with an HD cap of 20 for skeletons and 10 (of the base creature) for zombies.

[Segev]

Hydra make terrifying zombies.

[CryptbornAkryea]

I heard remorhaz was pretty sick as a skeleton. I'm thinking a beefed up, corpsecrafted skeletal remorhaz as a comfortable mount.

Also makes for a great entrance when going to see the king!

[Madara]

I'll just leave this here (http://www.giantitp.com/forums/showthread.php?223916-A-necromancer-s-playmate-The-guide-to-picking-the-right-Skeleton-Pet). Its a bit old and I probably could re-do the formatting, but I did go through a lot of books for it.