Also, I suppose we should differentiate between the three ways to see this power being used by players: 1) As part of collaborative storytelling; 2) As something that tends to happen around their character for some reason, but which their character has little or no control over although both might be better modelled by a mechanic related to narrative control, e.g. getting narrative control at a discount, but granting the GM action dice each time you use this discount); 3) As reality-shaping powers which their character actively directs.
In terms of 1) I'd handle this by allowing the players to request "Campaign Quality X" until the end of scene, and if the GM approves, the group pays 1/2 the AD cost 2) Mechanically, I'd treat that as a Subplot + liberal use of narrative control dice 3) That would probably count as some kind of reskinning of magic or psionics.
I mean, I'd call that a ritual complex check way before I made it an origin.
Sounds doable as well - could you spell out how you might run this?
In my home games, I use rituals as narrative devices / ticking timebombs that the PCs have to interact or contend with more than I use them as PC-initiated ones, but that's really just a difference of approach.
From a GM's perspective, I guess step 1 is the Who/What/When/Where/Why to explain the ritual's place in-setting. Most importantly, I'd want to identify what's powering the ritual -- is it a whole valley full of believers? Is it blood? etc.
If a player were to initiate a ritual, regardless of the effect if successful I would have it follow a format similar to this, with a lot of room for variation within each step:
1) Research the details/requirements/specifics of the ritual (likely using Investigate, possibly multiple Investigate checks, possibly requiring traveling/finding lost knowledge/whatever to allow the character to attempt the Investigate/Research in the first place)
2) Acquire resources/relics for the ritual (From as simple as a Haggle check to as complicated as questing to locate key components, etc.) -- lot of room for variation here
3) Preparation (Drawing sigils, preparing the site/sacrifice, or even waiting for the weather to be right or planets to align) -- again, plenty of room for variation, but you could easily use this a skill check for this -- Crafting, Spellcraft, or even Survival might be appropriate, depending on the ritual.
4) Execution (Depending on the complexity and length of the ritual, this could be a single check, this could be a series of checks. Impress, Spellcraft and Resolve would be the skills I'd be most likely to call for, especially Resolve for longer rituals since concentration and attention to detail are kinda important)
For example, in my home game, the PCs have a plan to call a demonic avatar (The Reaper from Cleansing of Black Spur) and entrap it, sealing it away from the mortal plane. In my notes preparing for this, I've basically set it up using the above format:
Research - the Sage has been studying the Infernum they captured as part of that adventure to learn how to accomplish the calling and binding.
Acquisition - to call and hedge the demon while finishing the ritual of binding, the PCs need to obtain Demon-Spires crafted out of rare metal.
Preparation - Once the PCs are ready, they'll have to find a suitable place to conduct the ritual, prepare the trap, align the demon spires, draw their protection wards, etc.
Execution - I'm going to handle this as multiple checks -- 1 to conduct the calling, then a TBD number of successful Resolve checks to complete the ritual while the rest of the PCs will be battling the demon to hold it at bay long enough to give the Sage time to complete the ritual.
The result at the end (or potentially anywhere in the middle) of the ritual can be whatever I want it to be -- continuing the example once the demon is called, it will immediately trigger a Dramatic Scene. You could just as easily rule that after the first of the Execution checks, any campaign quality is in effect until the end of the ritual or scene. In general, I'd handle this on a case-by-case basis rather than trying to over-burden it with specific rules