it has always bugged me that there weren't rules included for complex magical rituals so we made some complex magical rules for rituals. Feedback as always is appreciated and encouraged.
Rituals
A ritual is a long and complicated endeavor that a group of casters can choose to undertake in order to cast a spell that is otherwise unavailable to them. This is usually done by several lower level casters wishing to cast a spell too powerful for any one of them to cast alone, but this isn’t a universal truth.
Class and Caster Level of the Ritual
The first consideration is that all participants of the ritual must be of the same caster class. The reason for this is that they all need to cast magic in the same way in order to cast cooperatively. The participant with the highest caster level is considered the ritual leader.
Using the class of the participants, determine the lowest caster level needed to prepare and/or cast the spell they wish to activate using the ritual. That caster level is the total number of caster levels the group needs to equal (or exceed) in order to cast the ritual.
As an example, Wish is a 9th level sorcerer/wizard spell. We’ll continue to use this spell as the example from here on out. The earliest level a wizard is able to cast it is 17th level, and a sorcerer at 18th level. Therefore, if the ritual participants were wizards, their wizard class levels would have to equal 17 ( A level 9 and a level 8. Or three level 4’s and one level 5. And so on.) The same for a sorcerer, except they’d need one more caster level, since they can’t cast 9th level spells until 18th level (Two at level 9. Or three level 2’s, one level 5, and one level 7. Etc).
Length of Time
Now, you need to determine the length of the ritual. A ritual lasts a number of hours equal to double the caster level of the spell minus the caster level of the ritual leader. A Wish cast by wizards with a level 10 wizard acting as the ritual leader would last 24 hours (17th caster level x 2 - 10 for the level of the leader).
Each additional participant that adds caster levels above the minimum needed, and isn’t necessary for the casting of the ritual, adds one hour to the ritual’s time. The caster levels are added from highest to lowest. For this reason, the first participant who exceeds the needed caster level for the ritual isn’t counted as adding an hour to the ritual if removing them would take the caster level below the needed amount. This makes them necessary for the ritual to function and therefore not an ‘additional’ participant.
So in the case of a level 16, a level 7, three level 5’s, and two level 3 wizards casting Wish, the level 16 is counted first. He needs one additional caster level in order to cast the Wish ritual, so we add the level 7 next. They now meet the caster level requirement. The three level 5’s and two level 3’s add an additional 5 hours to the ritual because they aren’t actually needed. This would make their ritual take 23 hours (17th caster level x 2 - 16 for the level of the ritual leader + 5 for the additional participants)
Determining the Difficulty
Now that you’ve determined your caster class, caster level of the ritual, number of participants, and time of the ritual, you’re ready to figure the spellcraft DC needed for the ritual to succeed.
As stated earlier, the participant with the highest caster level is considered the ritual leader and they’ll be the one to make the spellcraft check at the end of the ritual to determine whether or not it was cast successfully. The other participants do NOT give any bonus to this check,
The base difficulty of a ritual is 20 + the spell level + 1/hour of the ritual.
After determining that, adjust it by adding 2 to the DC for each participant in the ritual, excluding the ritual leader.
If the total caster level of the participants exceed the needed caster level to perform the ritual, add the excess caster levels together, divide by 2 (round down) and reduce the total DC by that number.
To reduce the DC further, lives can be sacrificed as a part of the ritual. Each level (minimum 1) that is sacrificed reduces the spellcraft DC by 1 (A level 5 fighter would reduce the DC by 5). If the victim is an NPC class, you count ¼ of his levels off the DC (minimum 1). In the case of a level 8 Commoner, the DC would be reduced by 2.
Concentration and Interruption
Because rituals require so much focus and dedication, the longer they go on the harder they are to maintain.
After the first 12 hours, all participants must make concentration checks once an hour, every hour. These checks begin at DC 10 and go up by 1 every two hours. If you succeed by 10 or more, you can choose to give a +2 to another member of the ritual on the following check. If any
member fails their concentration check, the ritual is interrupted.
If a ritual is interrupted for any reason before completed, the ritual fails. All casters involved are depleted of their magical energies for the day (all prepared spells or spell slots are expended) and they’re fatigued for a number of hours equal to the time left in the ritual before it was interrupted.
Combined Ability Scores
A ritual cannot be completed if the casters involved do not have a high enough combined ability score to cast that spell.
To determine the combined ability score, start with the ritual leader’s primary casting ability (Intelligence for wizards). Now separately add the MODIFIERS of the rest of the participants and divide by 2 (round down). Add this number to the ritual leader’s ability score.
For example, the ritual leader has an intelligence score of 16. The other two participants helping him have int scores of 16 and 14. Take their modifiers (+3 and +2 respectively) added together (for a total of +5) and divided by 2 (which becomes a +2 after rounding down) and add that to the ritual leader’s int score of 16 (which becomes 18 with the +2). The end result will look like this: 16 + {(3 + 2) / 2} = 18. This group has a combined modifier of 18, meaning they can cast up to 8th level spells at the highest.
Multiple Spells and Past 9th Level...
For rituals involving multiple spells, the overall spell level is equal to highest spell in the ritual + 2 for each other spell involved. So combining a 9th level, a 6th level, and a 5th level spell would be the equivalent of a 13th level spell for the ritual’s purposes.
When determining the caster level for 10th level spells and up, assume the caster level is 20 + 3 for every level above 9th. A 10th level spell caster level would be 23, 11th would be 26, 12th would be 29, and so on. Use this caster level for all above considerations such as DC or time needed.
Additional Considerations
A rituals needs the normal components listed for the spell(s), as well as another 1000 gold per level of the spell(s).
The spellcraft difficulty for an outside observer to determine the spell effects of a ritual are 20 + spell level + 1/person involved in the ritual's casting.
A spell with a target of personal can only be used in a ritual if the target is the ritual leader. Additionally, the leader needs to be able cast the spell being used.
In order to make a ritual permanent, the Permanency spell must be included in the ritual (not cast afterwards) and 20,000 gold worth of diamond dust must be added to the material components used for the ritual.
To determine how multiple magic effects work together in the ritual, use the guidelines under Combining Magic Effects in Chapter 9: “Magic” of the Pathfinder Core Rulebook.