Thursday, May 13, 2010

The Moon Pool

I'm a big proponent of including locations of special interest in my dungeons. Generally, these are mysterious and/or beneficial places that hold something that brings the characters back to it again and again. An oft-mentioned example of this from the Dwimmermount campaign is "the Cleric Tree," a weird, azoth-warped subterranean growth that, if properly tended to, yields "fruits" that function as potions of healing. Early on in the history of the campaign, the party discovered this growth, unlocked its secrets, and regularly returned to it in order to take advantage of its boons. In practical terms, this meant that, even as the characters delve deeper into Dwimmermount, they still have reason to return to earlier levels, which in turn gives me the opportunity to present the place as a living environment rather than a static one that can be "cleared" with enough effort. To my mind, this presentation is one of the key differences between a "megadungeon" (or campaign dungeon) and a mere "dungeon" (or lair).

Another special interest location is the Moon Pool, a shallow pool in a series of caves inhabited by a tribe of mutant kobolds. The cave in which the Pool is located has a small opening in its roof through which moonlight can shine, reflecting in the Pool. The Pool itself holds what alchemists refer to as "true water," a primordial liquid untainted by physical contaminants and that cannot be destroyed or have its state altered. Thus, it does not evaporate and cannot be frozen with even the mightiest of spells. On the other hand, true water is a supernatural solvent (which is why alchemists prize it), dissolving magical energies within itself.

In the case of the Moon Pool, the magical energies it dissolves are moon rays, called "lunar emanations" by sages. These moon rays may then be imbibed by living beings who partake of the Pool's contents, boosting -- or diminishing -- their magical potency, in accordance with the phases of the moon, whose power over magic is well-known. Drinking from the Moon Pool has the following effects:

Random Roll (1D20)

Lunar Phase



New Moon

-1 caster level, -1 spell (lowest and highest levels)


Waxing Crescent

+1 caster level


First Quarter

+1 spell (lowest level)


Waxing Gibbous

+1 spell (highest level)


Full Moon

+1 caster level, +1 spell (lowest and highest levels)


Waning Gibbous

-1 caster level


Last Quarter

-1 spell (lowest level)


Waning Crescent

-1 spell (highest level)

"+1 caster level" means that, for spells that have variable effects based on level (e.g. fireball), the caster is treated as one level higher than he actually is. "+1 spell" means that the character gains an additional spell of the type indicated (lowest/highest level) for the duration the Moon Pool's infused water is in effect. Obviously, effects stated as a penalty (e.g. "-1 caster level") function in reverse.

A character who drinks from the Moon Pool must make a saving throw against Spells or Radiation. Success indicates that the effect listed above is operative, according to the current phase of the moon. The effect lasts for a number of days equal to 1 plus the difference between the saving throw number and the number rolled by the player for his character. For example, a 6th-level magic-user requires a 12 to save against Spells or Radiation. If his player rolls 14, the appropriate effect lasts for 3 days. Failure means that the appropriate effect is not operative and no subsequent drinks from the Moon Pool will have any effect whatsoever for a number of days equal to the amount by which the character failed his saving throw. For that matter, while one effect is operative, subsequent drinks provide no additional effect, good or bad. Finally, Moon Pool effects cannot be dispelled by any known means; a character who has drunk from its waters must wait until the appropriate number of days has passed before its effects will fade.

I keep pretty good track of time in my campaign, using the guidelines given in Volume 3 of the LBBs. Consequently, I know roughly what phase the moon is in if it ever becomes pertinent to play. However, not all referees are as fastidious about timekeeping and so the table above can also be used to randomly determine the current phase.


  1. Totally cool! This is the kind of thing that make D&D, D&D.

  2. I love stuff that's both good news and bad news for the PCs - but which they might keep coming back to once they figure it out. I also like the fact that the effects could last for just a day or for a really long time, depending on how badly I fail my save...

  3. Cool. Always fun to work out what I drank. <grin>

    [Actually one of the things about OD&D is that you don't really mind drinking strange waters or eating strange fruit to see what happens. If it turns out you shouldn't have, well there is always the next character. But when the character is the focus of the story you become less cavalier about risks to the character. "What do you mean the heir to Fandonia just died? Ummm errr. Doesn't he have a another long-lost brother somewhere?"]

  4. Cool ... Just curious, I don't think from your write-up that your players come across the Pool yet. But what kind of clues, if any, will there be to working it when they do? (I am interested in clues and tricks these days having written a bit about the matter here.)

  5. I can only think of one word that describes my thinking upon reading this post: YOINK!

  6. Very nice.

    On the other hand, true water is a supernatural solvent (which is why alchemists prize it), dissolving magical energies within itself.

    And thus it's effective against magic weapons and items, a foiler of wards? My long-time Chaotic Neutral F/MU/TH would be very tempted to experiment with this.

    A tendency that often got him into trouble. :)

  7. Hmmm...I think you forget about another power of the Moon Pool. It ends campaigns! Just look what happened over at OD&D discussion after we found it. The DM evaporated and all the PC's were forever frozen in time! Beware the Moon Pool!

  8. Agreed, YOINK. These are perfect for one of my campaigns. I'm always looking for interesting locals

  9. > using the guidelines given in Volume 3 of the LBBs

    This? Seems rather thin and "gamey".

    Dungeon expedition 1 week
    Wilderness adventure = 1 move = 1 day
    1 Week of actual time = 1 week of game time

    The time for dungeon adventures considers only preparations and a typical, one day descent into the pits.

    The time for Wilderness expeditions would include days of rest and recuperation.

    Actual time would not be counted off for players "out" on a Wilderness adven-
    ture, but it would for those newed in their dens, hideholes, keeps, castles, etc., as well as for those in the throes of some expedition in the underworld.

  10. I totally dig this idea.

    The only part I don't like is using the differential of the saving throw roll from the target number to determine the effect duration.

    I will likely just use 1d6 for this.

  11. the "magic pools" trope is sooo much D&D.
    I put at least a few every campaign, as either fountain, fruit trees, streams, pools to bathe into, wishing wells and so on. Possibly with different effects depending on how they're used (drink/bathe/temper steel/water plants/plant seeds from magic fruit).

    My favourites are the trees in Forgotten Temple of Tharizdun and the fountains in the Tower of Zagyg (Greyhawk Ruins).

  12. But what kind of clues, if any, will there be to working it when they do?

    It's not clear in the description, but the water in the Pool radiates a bluish-purple haze and detect magic indicates that it is indeed magical in nature. Beyond that, though, it's mostly a matter of trial and error to determine its precise effects, though, if the players took it back to Adamas to have it analyzed by a sage, I'd give them a lot more information.

  13. This is excellent! I think I'll also borrow this for my game.

    Question: I really liked the picture you posted. Do you know the author? Maybe I can find one in larger resolution...

  14. The concept of special locations where you can return to is also one that I'm exploring in my megadungeon. Sometimes the room provides immediate benefits, often it is merely awaiting the players to unlock its secrets. They will return to it again and again if enticed enough to try and solve its mysteries. When they do, the payoff will have to be enough so they return in the future. In my case, is an orb of knowledge that I've placed in a room on level 1.