No; the name is based on the fact that most beings trying to become one need to trust their partner who is performing the ritual on them a lot, to the point that they often form pacts with one another to, essentially, not make a "mistake" in the ritual and destroy them instead of empowering them. It does not (usually) involve pacts with extra-dimensional forces.
EDIT: Well, besides the one that contains the instructions for the ritual, but there aren't any new ones formed, nor is the old one directly involved.
Indeed. Is there something wrong with that?This appears to be an epic level creature.
I actually wanted a template to be applied to an undead creature that meets the (very heavy) prerequisites (some of which were mentioned in the request, but others can be added if the person making it wants to.) It should have a high CR adjustment, though I'm not sure how high. Anywhere from +5 to +10, I guess.CL 21 seems a bit excessive. Create greater undead can be cast by level 15. What CR are you aiming for?
You seem to be misunderstanding. This doesn't destroy them both, or combine them, or anything like that; it merely requires one powerful (read: Epic) undead spellcaster to be the subject of a ritual (outlined very briefly in the request) that can only be performed by another (equally powerful) undead spellcaster (both typically being liches, though other types are possible.) That said, the ritual is so blasphemous that merely knowing how the details would melt the brain of a living creature out through their ears and tear their soul into several pieces (hence why only another undead can perform it) so heck yes it's an Evil act!The problem I have with this is the requirement that it requires 2 undead creatures to create. The corpse of an undead creature could be resurrected, so I would suggest that creating this would be an evil act. Did you have any particular creatures in mind?