Oh my GOD do I actually have to explain this. Okay. Let's do this. So. There are many, many universes, and because the Tesseract's a jerk, we're having to interact. Because you have many categories of undead in your world does not mean that there are many categories of undead universally. The rules of your reality don't reign supreme. You can use the fact that I don't know YOUR rules as proof that I'm an idiot all you like, but all it proves is that I'm from a different set of rules entirely.
Now, if you want to go another round of "NO, U!!!11", be my guest.