Mana powered Magic does not work on worlds with no mana but magic powered by other things (Sanctity or Psi) can. Note that Mana Enhancer changes this somewhat.
Very High ManaEdit
Anyone who knows spells can cast them. Very high mana worlds make magic common and more potent, affecting some rules. First, a mage who spends FP (Fatigue Points) to cast a spell on his turn gets those FP back at the start of his next turn. Second, all failures are treated as critical failures – and actual critical failures produce spectacular disasters!
Anyone who knows spells can cast them.
Only mages can cast spells. This is the default mana level in most fantasy settings: mages use magic, others don’t.
Only mages can cast spells. Low mana worlds make magic rare and less potent, affecting some rules. First, all spells perform at -5 to skill, for all purposes. Magic items are similarly affected; see Power of a Magic Item  Second, critical failures have mild effects or no effect at all.
Very Low ManaEdit
Only mages can cast spells. All spells perform at -10 to skill, for all purposes and magic items require a power of at least 25 to function.
No one can use magic at all. Magic items do not function (but regain their powers when taken to an area with mana). This mana level occurs in isolated spots in magical worlds, but entire worlds can lack mana, making mana based magic use impossible.
Special Forms of ManaEdit
Continuous Mana is where the gradation from very low mana to very high mana is more gradual going from -10 to +10 to skill.
Variable Mana is where the mana level of an area fluctuates such as in regards to the time of day, the season, or weather.
Aspected Mana is mana that functions as higher effective mana with regards to “aspected to” spells but lower effective mana to spells it is “aspected against”.
In an area of Wild Mana "any success on a spellcasting roll counts as a critical success, and costs 0 FP, while any failure is treated as a critical failure, with the spell’s full normal energy cost."
Twisted mana is so weird that it causes magic to behave in an unpredictable, even perverse way. Spells are cast at -2 in addition to any other penalties.
Spells cast in Mana of this type do not cause fatigue but instead are counted against a threshold total (default is 30). The spell that first brings the mage's tally over Threshold triggers a Calamity Check with a +1 on the 3d for every full five points by which Threshold has been exceeded. All spells cast once Threshold is reached trigger a Calamity Check. "Once per day, the mage's Tally is healed by an amount equal to his Recovery Rate (RR). The "default" RR score is 8, with recovery occurring at sunrise."
- Q If a mage casts a spell and spends a point of fatigue to end it prematurely, is this fatigue from spell casting? Is that renewed immediately in a Very High Mana zone?
- A No. That's physical fatigue. It's not reduced for high skill, so it's not really a "mana" cost at all.
- ↑ Basic Set, p. 481.
- ↑ GURPS Thaumatology 58]]
- ↑ GURPS Thaumatology 43-45, 59
- ↑ GURPS Thaumatology 76-80