Arch lich?

Hmmm,an undead deity, undead tarrasque, or, the pact to summon me would be the life of the summoner and he summons me as his undead self.

I like all of these options

Whatever kind of undead Raziel counts as. Double undead vampire = soul devouring wraith? Hey, manifesting on both spiritual and physical realms is neat.

Probably like a skunk or something idk.

Skeleton:

• When the hero comes into the tomb, I want it to be dead first, no faffing about with boss fight (which they always win) BS.
• I like the musical nature of their bones.
• I already am one, sort of...

If there are no restrictions other than "undead", I suppose that one can probably min-max this to be some sort of undead god.

I have little familiarity with Dungeons & Dragons' Greyhawk setting, so I don't know if "being Vecna" in particular is a good idea, but it illustrates the point that that game clearly has undead gods.

I would be the kind of ghost that could possess people so I could bang their wives using their bodies but somehow when I cum, the possessed penis shoots out my actual sperm so I can forever keep my sainted genome alive

One that can shape-shift so I can change my bodies sex to the one that aligns with my gender identity and be fully conscious and self aware but I'd also line to have free will

I'd also want to have all powerful magic as well

Alhoon

I guess a skeleton. Id be reach on account of all the bones

Oh hell no. A fumbled 1, shambling back into sweet death-death within moments, possibly dragging him with me.

Tiamat

The kind that instantly kills the necromancer, then returns to being dead.