OpenQuest: Metered Thaums (a.k.a. Limited Mana)

Posted: 2023-06-13
Last Modified: 2023-07-01
Word Count: 1132
Tags: d100 openquest rpg

Table of Contents

2023-06-27: Renamed Mana to Thaum(s), Limited Mana to Metered Thaums, and Mana Meter to Thaum-o-meter. I’m not sorry.

2023-07-01: Corrected some search-replace errors when I switched from “mana” to thaum(s).

Ironically inspired partially by “Unlimited Mana”, this article will outline an approach to limit spells in the “One Magic” system without counting Magic Points. It will require some counting, though.

I previously described the justification for this mechanic thus:

… every spell cast[] uses up mana / weakens reality / angers the spirits / (insert excuse here), so casting too many spells in a period of time increases the likelihood and intensity of a “backfire”, or Calamity as the UMana article calls it. The only solution is to let ambient mana / reality / spirits / whatever recover at some fixed rate.

Basic Rules

Rule Changes

Before we get to the “Metered Thaums”1 rules, let us first rewrite a rule in standard One Magic:

Metered Usage

Every magic-using character has Thaum-o-meter, represented by a rising count of “thaums” on a piece of paper, pennies or other tokens in a bowl in front of the player or GM, a drawn clock face, an actual clock face cannibalized from a broken clock, etc. The simplest apprach would be to increase the count by one for every spell the character cast, but one could do something more complicated. For example:

Spell Qualities Thaums
Common 1
Taught 2
Secret 3
Critical Success +1

Every time a magician successfully uses a spell, the GM or player updates the magician’s Thaum-o-meter.

Note that the GM may keep a single meter for all their magic-using characters or count each character separately. It depends how many characters use magic and how badly they want to see a catastrophe.

Catastrophe Table

Every time a magician rolls a Critical Failure, roll 3d6 and add the result to their current Thaum-o-meter reading. Then look up the total on the chart below.

Thaums + 3D6 Effect
< 4 No effect
5-13 The spell’s effect rebounds on the caster. If that’s a good thing, it instead affects a random enemy or friend, whichever is worse.
14-17 The caster loses the use of this spell for one hour of game time.
18-21 The caster is struck as if by the Mischief spell.
22-24 The caster’s hair turns white permanently. If it’s already white, roll again.
25-26 The caster cannot speak or cast any spells for the next hour of game time. If this result comes up again, extend it by an hour.
27-29 The caster takes a -20% penalty on all skills for the remainder of the session. If rolled again, increase the penalty to -50%. If rolled a third time, reroll.
30-32 The caster loses the use of this spell for the remainder of the session.
33-35 The caster is cursed so that all Magic Casting failures provoke a roll on the Catastrophe Table. Subtract five and roll again for an additional Catastrophe.
36+ The caster is cursed so that all further uses of magic provoke a roll on the Catastrophe Table. Subtract five and roll again for an additional Catastrophe.

Yes, this table could be wackier. Or stranger. I’ll probably revise it at some point.


If the magician rests for a day, they may take 1d6 (or 3?) points off the Thaum-o-meter. This represents the fabric of reality around the magician recovering, the spirits calming down, the thaum supply replenishing, or however magic works in your world.


External Thaums

Thaums come not from the air or the magician but from a particular object: a Philosopher’s Stone, a magic wand or staff, a medallion, whatever. This object is the physical embodiment of the Thaum-o-meter: every use stores up bad juju, and its owner has to let it rest, soak it in blood, or whatever to bring the Thaum-o-meter back down. But without this object, the magician can’t use magic at all.

This option pairs well with Negative Thaums which gives the user some breathing room before the catastrophes start.

Negative Thaums

Instead of the Thaum-o-meter going continuously up, it starts at a Threshold value (like 20 per person) then goes down for every spell cast. When it reaches or passes zero and the magician rolls a Critical Failure, the player adds the amount the meter went negative (i.e. the deficit) to the result of a 3d6 die roll. So, for example, if the meter were at -8, the player would roll 3d6 and add 8.

Mathematically this is the same as simply subtracting the Threshold in under the “positive” default, but this may be easier for the mathematically challenged.

This option gives players a bit of slack before catastophes start happening.

Non-Renewable Thaums

In this option, the Thaum-o-meter won’t reset by itself. The player(s) must pray at a temple or shrine, slay a magic beast (to release its thaums), or simply move away with no forwarding address. (Ghosts can read.)

Shared Thaums

Instead of one Thaum-o-meter per character, there’s one Thaum-o-meter for the whole table. All magic use increases the same meter.

There are two positives, though:

  1. Subtract 10 per player character from the total of dice and meter before looking up the total on the Catastrophe table.
  2. The Thaum-o-meter resets to 0 whenever the characters leave an area. (If they return, the old meter value will remain.)

Shared Thaums recover at a rate of (number of players)d6 per day.

Variable Thaumic Level

Thaums are not an evenly distributed resource. In some places thaums are few or sluggish, in others they flow freely. The GM should use the following table to rate the thaumic level of a specific area … or time and place.

Thaumic Level Magic Casting Catastrophe Notes
NONE -100% none No magic is possible
Very Low -50% +20 Thaums flow weakly and/or sluggishly
Low -20% +10
Normal +0% +0 Ordinary thaums, no modifiers
High +20% -10
Very High +50% -20 Thaums flow freely and responsively
Ultra High +100% none All spells just work, no Catastrophes.
Thaumic Level
Name of the level.
Magic Casting
Modifier to the Magic Casting skill.
Modifier to the Catastrophe roll total.
Non-normative explanation.

New Spell: Sense Thaums

The caster can sense the Thaumic Level of this area as well as any unusual conditions like Shared Thaums or Non-Renewable Thaums.

Even if this spell fails, the caster will get some sense of the thaum level …

  1. I did not want to call this Mana. That’s a Polynesian word that does not mean what we gamers think it means. I’m using Thaum instead thanks to Terry Pratchett. ↩︎