Ghosts make their first appearance in AD&D, and were left out of the OD&D, Holmes, and Moldvay versions. In the Monster Manual, they’re powerful creatures indeed. Weighing in at 10HD, AC 0 (8 on the ethereal plane), they have a special attack of Magic Jar (a 5th level magic user spell) or of touch where their target ages 10-40 years when successfully hit. In addition, they can only be hit by magical or silver weapons (the latter of which only cause 50% damage). They can only by effected by magic spells cast from the ethereal plane, and any human or demi-human that they kill is “forever dead”. Presumably that means no Raise Dead, no Resurrection, no Reincarnation… no Wish? I think I read in 2nd edition that a Wish would work. Still, holy shit, huh? All of this is tempered by the fact that they can be turned by clerics… Of 7th and higher level. When I say 7th level, I mean with a roll of 20, although after that it does get easier quickly.
The MM’s description of its Magic Jar ability is not entirely clear to me. How often can they use this - is it “per the spell” as stated, implying once per day? The MM says that “if the ghost fails to magic jar its chosen victim, it will then semi-materialize in order to attack by touch…” So it’s not free to choose another opponent and try again? Maybe the supernatural effort to do so is too draining and that’s why the ghost has to materialize to attack in another way. Although it might be suggested that becoming tangible and visible would take supernatural energy as well, maybe even using more energy than just possessing someone’s body. Mentzer tries to clarify this a bit in the 1984 Companion Rules. There it states a ghost can use a magic jar effect, once per turn. Considering that the ghost would have the spell casting and general abilities and knowledge of the one possessed, it’s a formidable power however often it can be used.
What is this Magic Jar? It’s basically just good old fashioned possession, although the spell as written in the Player’s Handbook specifically involves the use of a large gem or crystal. This is where the spell caster first places his soul, or life-essence before eventually attacking and possessing someone. But why was the ghost’s power of possession written up this way? Are all ghosts inhabiting gems? That can’t be right. The MM describes them as “roaming about at night or in places of darkness.” Was using Magic Jar in its description just a way of easily referring DMs to a similar magic effect, and for brevity’s sake? Do I have to roll the ghost’s intelligence and wisdom in order to make the calculations listed under the Player Handbook’s entry for Magic Jar? The MM already says that they’re highly intelligent. Maybe Mentzer can clarify again. Back to the Companion Rules - he says this of their magic jar effect, “If successful, one item carried by the ghost will glow, powered by the life force of the victim. The ghost’s force then possesses the body of the victim and causes it to attack others. During this time, and for as long as it possesses another, the ghost’s figure stops, merely holding the light (but oozing the Ectoplasmic Net). The ghost and the item both remain ethereal.” Yeah. Ok, let’s look to a later edition - I just happen to have a copy of the 3.0 MM here. Ah, ghosts are now templates, and their power of possession is “similar to magic jar…although it does not require a receptacle.” Aside from potentially confusing things, a “magic jar” sounds a lot more innocuous than the Exorcist evoking “possession”.
Out of curiosity, I looked at Bruce Galloway’s interpretation of the ghost’s abilities in his Fantasy Wargaming book. Say what you will, but that book can provide a lot of perspective. Galloway says nothing about a ghost’s ability to possess someone, perhaps rightly assuming that only demons have this power. Instead, he refers to the ghost’s method of attack as its ability to frighten, period. This ability, depending on a number of factors, will either fail, cause a temporary loss in a character’s Bravery attribute, cause madness, or cause instant death. I like this, it’s very straightforward. Maybe it’s worth checking out yet another set or two of rules.
I looked at my (AH) Runequest’s ghost write up and see that there it engages in spiritual combat with intruders (it’s tied to a site or object). If it reduces its foe to zero magic points, it possesses him. Not surprising, but in a slight departure from the AD&D model, “usually causing the victim to kill himself.” I also looked at what Call of Cthulu has to say, and found my favorite entry thus far on the subject. “Each ghost should be crafted by the keeper to fit the circumstance of the adventure.” They may or may not be vulnerable to magic. They may or may not be exorcisable.
To many people, ghosts are real. More real to most people than ogres and orcs anyway. To me, that’s the appeal of using them in the game… they still stoke primal fears. The ghost and its powers also seem well suited to house-ruling the hell out of, or writing them up however you like. You might have to, depending on what game you play - there isn’t a ghost entry in the Swords & Wizardry rules, the 0e Reloaded Monster Book, or Labyrinth Lord.