If animated corpses, ghouls, wights and wraiths make up the common undead, D&D has always had room for more dangerous abdead foes, and unlike ghouls wights and wraiths, these more powerful undead are not simply increasingly dangerous versions of the same creature. It's unclear exactly what purpose greater undead, as I've taken to calling spectres, mummies and vampires, serve in Monsters & Treasure, are they tougher versions of wraiths and wights to threaten higher level players, are they puzzle monsters designed to threaten mid level parties in small numbers or leaders of undead factions? Whatever the intent powerful undead are an important part of the higher level random encounter tables and each represents a significant threat to characters. Following the trend established with Lesser Undead, the danger from the more powerful creatures is largely the result of immunity to some attacks and the ability of their attacks to do permanent damage in the form of status effects.
|Warhammer Fantasy has this wonderful way of breathing life into the cliche|
Mummies are strange creatures then, not much stronger then Wraiths, but more accurate and very slow (they have the same AC and 5+1 HD to a Wraith's 4), moving a a rate of '6', the same as zombies and skeletons. They have a seemingly less terrible special attacks then wraiths and wights, causing a disease rather than draining life force but they are invulnerable to regular weapons, not just missiles. It almost sounds like the Mummy is a stronger form of the animated corpse, the skeleton/zombie, rather then a quick, self-willed form of revenant like the ghoul, wight or wraith.
The most complex aspect of the mummy is it's special attack seems like a clumsy and confusing mechanic, especially in a system where a common convention is re-rolling HP at the start of each session. My own take on "Mummy Rot" is that the disease prevents magical healing and reduces HP total to 1/2 the rolled amount at the start of each session. I'd also add a permanent -1 to HP even if the rot is cured by cure disease spell, plus the rot is disgusting and makes the character smell bad. Obviously there's a lot of room for a far more horrible disease, something with statistics loss and progressive HP damage culminating in death. I'm not really sure if it's necessary as the consequences as written have a pretty nasty overall effect. The only plus side of death by Mummy as opposed to death by Wraith is that the victim of a Mummy will not rise as a Mummy.