Advice on Spirit-based RPM variant

[dfinlay]

I've been musing about a heavy modification of RPM and wanted to get some feedback on my ideas.

The fluff: Spells are actually cast by powerful spirits. Every location will have a collection of spirits that are present and some casters carry their own spirits with them. Casters preform elaborate rituals to gain the notice of spirits and gain their assisitance.

The mechanics:

It uses Effect Shaping with Ritual Adept prohibited.

The world is covered in overlapping domains of spirits. Almost everywhere will have one or more powerful spirits. Each spirit has the following set of characteristics:

A descriptor for spells used with them. This might be something like “Fire” or “Memory”. Spells must use a spirit that thematically fits with the spell (GM's call). Particularly complex spells may require multiple types of spirits, in which case finding a place where both classes of spirits are present can be an adventure in itself.

A maximum energy that they can handle. This will typically be quite high, so that the caster's skill will be what limits their power, but extremely powerful spells will require powerful spirits.

An attribute that combines with Magery to determine your Path skills. Some spirits must be reasoned with (IQ), some must be tracked down (Per), some must be mentally resisted/overcome (Will), some must be impressed with physical feats (HT/ST/DX). Some may also allow you to use certain advantages (Appearance/Charisma, for example). This applies even if the spirits already want to help you. It's just part of how spiritual magic functions.

A tradition (set of significant or mandatory modifiers) that works for spells with the spirit. Some may have more than one.

Some spirits may grant a bonus (used instead of places of power).

Some spirits may also have special rules that apply to magic when using them.

Most charms are symbols of promises made by spirits. As such, they cannot be triggered outside of the domain of the spirits used to make them. At an additional -4, the caster can create charms that instead trap a portion of a spirit. Spirits dislike the use of this, so unless it was negotiated ahead of time (and what the caster offers will have to be very good), further casting from the same spirit by the caster will give a -4 to all spells (does not stack with the other -4 if making multiple such charms) and the spirit may retaliate against the caster. Overuse of this can damage or even kill the spirit.

Some casters may have ally spirits or spirit guardians. These work as above with the following modifications:

The character is always considered to be in their domain. Anyone else is if they have skin contact with the character, but is at -4 to cast without the character's permission.

An example (very powerful) spirit:

Maltrus: Maltrus is the spirit of an enormous but dormant volcano. He is vengeful and destructive. His domain extends 100 kilometers in all directions around the volcano itself.

Maltrus counts as a fire and heat spirit and gives +2 to all spells that use fire or heat for destructive ends. He may also be used as a substitute for an earth spirit for tectonic or geological purposes, at -2, or for the purpose of causing nightmares.

Attribute: Will

Tradition: Hermetic Deacons. Maltrus also appreciates human sacrifice, especially by burning. Involuntary sacrifice counts as double the normal bonus and voluntary sacrifice that kills the subject counts triple.

Energy limit: 5000 energy

The locals believe that Maltrus must not be invoked without first performing the slumbering ceremony, a ritual involving at least one singer, one drummer and nine dancers, as well as a shaman with Religious Ritual. Failure to do so supposedly runs the risk of awakening him and causing an eruption.

My questions:

Any thoughts? Anything you would add to such a system?
How should I price the advantage of having a spirit guardian?
Any thoughts on how I should do Paths? Path of Spirit and Path of Magic are especially problematic, given that all magic is spirit-based. I'm also not a big fan of Path of Undead.
It seems like this all is a pretty big nerf to RPM. How do you think RPM casters will hold up in a campaign with TL0-1 mundanes and Sorcery? (Humans get spiritual RPM. Fae get Sorcery.) I feel like the versatility of their magic should still make them viable and competitive, but I'm not sure.
I couldn't see the rules for Involuntary Sacrifice with Effect Shaping. Are there any? If not, what would be reasonable?

For the record. I have Laws of Magic, RPM and Thaumatology.