Please correct me if I'm wrong:
To create a variant skeleton, you need to have a CL = to the HD of the variant skeleton when casting animate dead. Nothing more.
To create a variant zombie, you need to cast a particular spell along with animate dead. Nothing more.
In short, I can't find anything in the zombie entry that says that variant zombies count as double HD, and I can't find anything in the skeleton entry that says you need additional spells.
Also, skeleton templates can be stacked, but zombie templates cannot, correct? I can't find anything in the zombie entry saying that they can be stacked (like it does in the skeleton entry).
One last question: When stacking skeleton templates, does the HD limit also multiply? Is a bloody burning skeleton worth 4x HD?
EDIT: What Charisma score does a bloody burning skeleton end up with? 12 or 14?
These variants are starting to look very shoddily worded.