Powers: Theurgy

Powers: Theurgy

In D&D slang, a theurg is a class that combines the powers of two different spellcasting classes, such as the mystic theurg (arcane/divine), psychic theurg (divine/psionic), soulcaster (arcane/incarnum), etc. In my setting, there are many different power sources, but taking two separate Sorcerous Empowerment advantages, for example, to make an arcane/divine theurg is a very suboptimal thing to do. However, I like the concept of such supernatural power blending, so let's try to come up with some rules for that to make such concept more attractive.

First, let's define a new term.

Controlling skill - skill that is used for hardcore improvisation for Sorcery-based systems (by default this is Thaumatology, but it can vary from setting to setting and from one spellcasting tradition to another), or a generic power knowledge skill for systems not based on Sorcery (such as Expert Skill (Psionics) for psionic powers, Expert Skill (Incarnum) for incarnum powers, etc.)

Now, let's create ways of blending these powers. Each one is a perk. You must specialize by combinations of power sources.

       Theurgy (Talent Sharing) [1]

    Whenever you use an ability or cast a spell, if you possess abilities of another power source (secondary source) with a theme appropriate to the ability being used or a spell being cast, you can roll against the lowest controlling skill of your power sources and add a number of Talent levels of the secondary source up to the margin of success on your roll to use the ability or cast the spell. This use costs an additional 1 FP that may be spent using both ordinary FP or ER of any of the power sources being used.

    Example: You have Sorcerous Empowerment, Sorcery Talent 2, and Thaumatology-12. You also have some psionic abilities, Telepathy Talent 1, Psychokinesis Talent 3, and Expert Skill (Psionics)-14. You decide to cast Shape Fire 1 (GURPS Thaumatology: Sorcery, p. 16). Since it fits the psychokinesis theme, you decide to add your Psychokinesis Talent to it. You spend 1 FP and make a roll against Thaumatology-12, because it is the lowest of your controlling skills. The roll results in 10, and that means that you may add 2 levels of Psychokinesis Talent to your Sorcery Talent when casting the spell, for a total of 4 levels of Talent. Were you to cast, for example, Planar Visit (GURPS Thaumatology: Sorcery, p. 16), you wouldn't be able to do this feat, because Planar Visit does not fit under the theme of telepathy nor psychokinesis.

      Theurgy (Shared Improvisation) [1]

    Whenever you improvise a spell using a Sorcery-based system, if you possess abilities of another power source (secondary source) with a theme appropriate to the spell being improvised, you can roll against the lowest controlling skill of your power sources and add a number of levels of Sorcerous Empowerment from the secondary source up to the margin of success on your roll for the purpose of determining what spells you can improvise. If the secondary source is not based on Sorcerous Empowerment, then its effective Sorcerous Empowerment level equals to one tenth of its most expensive ability's cost, rounded down. Note that you become unable to use abilities of the secondary source until you switch to another spell. This use costs 1 FP that may be spent using both ordinary FP or ER of any of the power sources being used.

    Example: You have Sorcerous Empowerment 3 (Limited Colleges, Fire, -40%) and Thaumatology-12. You also have Pyrokinesis 2 [28] (GURPS Psionic Powers, p. 56) and Expert Skill (Psionics)-14. You decide to improvise Ignite Fire (Improved) (GURPS Thaumatology: Sorcery, p. 16). This spell's full cost is 4 point, which is too high for you to improvise normally. However, this fire spell shares the theme with Pyrokinesis, so you decide to try to increase your improvisational limit. Pyrokinesis is a psionic ability, not based on Sorcery, so its effective Sorcerous Empowerment level is 28/10 = 2. You  spend 1 FP and roll against Thaumatology-12, because it is the lowest of two of your controlling skills. You roll 11, which allows you to add 1 to your improvisational limit. This is enough, so you improvise Ignite Fire (Improved). However, until you switch to another spell you lose the ability to use Pyrokinesis (and other Psychokinesis abilities, if you have them).

     Theurgy (Shared Reserves) [1]

    If you have abilities of different power sources and ER of different power sources, upon using an ability that costs FP, you may roll against your lowest controlling skill to instead use ER of a secondary power source, if the ability or spell being used is thematically appropriate for that source. If you fail, the ability fails.

    Example: You have Sorcerous Empowerment (Limited Colleges, Communication and Empathy, -40%), ER 10 (Magic), and Thaumatology-12. You also have some psionic abilities and Expert Skill (Psionics)-14. You decide to use the Broadcast technique for Telesend (GURPS Psionic Powers, p. 60). Using psionic techniques costs 2 FP, but you do not want to spend actual FP and want to use ER. Telesend is thematically appropriate for the college of Communication and Empathy, so you roll against Thaumatology-12, because it is the lowest of your controlling skills. You succeed and use up 2 points of ER (Magic) to augment your psionic ability.