Here are the ritual rules from OGL Horror. As you can see, they are fairly simple and straighforward, and its pretty easy to make up new rituals. The Exorcism ritual is from the book. The Seance ritual is one I wrote.
Rituals
Rituals are usually found in ancient books of occult lore, decoded from glyphs on the walls of tombs, or derived from mathematical formulae. They are a form of ceremonial magic, requiring only belief and the proper words and gestures from the participants — it is not necessary to comprehend how the magic works.
Each ritual description has the following elements:
Ritualists: The number of characters required to perform the ritual.
Primary: Each ritual has a primary caster who leads the ceremony and a number of secondary ritualists who aid the primary. The primary character must make a roll of some kind (usually Knowledge [Occult]) or a Wisdom or Charisma check against a DC.
Secondaries: Each secondary ritualist must also make a check of some sort. For each secondary who succeeds, the primary caster gets a +3 ritual bonus to the roll (and these bonuses stack with each other).
Requirements: Any special qualities that the primary or secondary ritualists must possess.
Components: Any special items that must be present for the ritual.
Costs: Some rituals drain hit points, ability scores, or some other aspect of the characters.
Casting Time: How long the various parts of the ritual last.
Effect: What effect the ritual has, if effective.
Failure: What happens if the primary ritualist fails his check.
Sample Ritual: Exorcism
This ritual drives out demons or evil spirits possessing a victim or inhabiting a building.
Ritualists: The ritual calls for at least one priest or similarly qualified primary ritualist (6 or more ranks in Knowledge [Theology and Philosophy] or Knowledge [Occult] is acceptable) as well as two to five assistants.
Primary: The primary must make five opposed Will saves against the demon. The demon may add its Hit Dice to its rolls; the primary may ad his Charisma modifier and gets a +2 synergy bonus if he has 6 or more ranks in Knowledge (Theology and Philosophy).
Secondaries: The secondaries need only succeed at a Madness save (DC 10) to successfully aid the primary ritualist. (Note from Erica: Madness saves are part of the OGL Horror rules and can be replaced with a Will save if you like or another Knowledge check for each secondary.)
Requirements: The primary gets a +5 circumstance bonus if he knows the demon’s true name or if he has some other hold over the spirit..
Components: Bell, book, and candle, as well as something symbolizing purity (salt is commonly used).
Costs: Once the fifth Will save is made, the primary takes temporary Wisdom damage equal to the hit dice of the demon.
Casting Time: One minue (12 rounds) of chanting and preparation, followed by the clash of wills between entity and primary ritualist. Each clash (opposed Will save) takes one round, with a one-round gap between.
Effect: If the primary ritualist wins the majority of the five opposed Will saves, the entity is banished. If it is an Outsider, it is forced to return to its place of origin and may not return unless summoned. If it is a ghost or other entity tied to this earth, it is disrupted for 10d10 months or is wholly destroyed, depending on how strongly the entity was tied to this world.
Failure: If the primary ritualist fails by more than two Will saves (ie. The entity won by a margin of 4-1 or 5-0), the entity may choose to possess him instead. The two must make another opposed Will save (and remember that the primary ritualist has now suffered temporary Wisdom damage). If the primary ritualist fails this save, he is possessed.
Séance
This ritual enables someone to open herself to supernatural forces and act as a beacon, calling out and bringing in haunting ghosts or other spiritual entities.
Ritualists: A séance requires a circle of at least 2 people.
Primary: The primary must succeed on a DC 20 Charisma check in order to make her presence known to ghosts, and invite them to communicate. The primary gets a +2 synergy bonus if she has 6 or more ranks in Knowledge (arcane lore).
Secondaries: Each secondary in the séance chain that succeeds on a DC 10 Charisma check provides a +2 bonus to the primary’s Charisma check.
Requirements: The primary need only have some knowledge of the occult and spirits — she must have at least 1 rank in the Knowledge (arcane lore) skill. If the primary has psychic feats, she can use them to see or influence an attending ghost (see the descriptions of the psychic feats).
Components: None. The primary and secondaries need only link hands and concentrate.
Casting Time: Performing a séance requires 1d6 minutes of mental preparation on the part of the primary, plus 2d10 minutes of time during which the primary calls out to the spirits and beckons them forth.
Effect: If the primary ritualist succeeds on a DC 20 Charisma check, a ghost responds to her call.
If the séance is held in a place known to be haunted, the answering ghost will be the most powerful entity in that area (measured by Hit Dice) or the specific entity named, whichever condition applies.
If a séance is held in a place that is not haunted or where a haunting is only suspected, the primary must call a specific entity by name. Otherwise, any entity may answer the call. The latter is a potentially dangerous situation that should only be attempted by a primary that is certain she can control the answering entity.
Once called, a ghost remains for a number of minutes equal to its Charisma modifier plus 1d4. The primary can dismiss a ghost before that time expires by making an opposed Charisma check against the ghost. Dismissing a ghost is a standard action. If the séance chain is ever broken, such as by a member of the chain releasing her partners’ hands, the ghost must succeed on a DC 20 Will save or be instantly dismissed. A dismissed ghost cannot be summoned by a séance or manifest for 24 hours.
Failure: If the primary ritualist fails the Concentration check by 5 or less, no ghost is called and the séance is a failure. If the primary ritualist fails by 6 or more, the results can be disastrous. The GM is free to interpret the consequences of a failed séance as he sees fit. One possible consequence is that a hostile entity — such as an evil ghost or even a minor demon — answers the call.
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Open Game License v 1.0a Copyright 2000, Wizards of the Coast, Inc.
Modern System Reference Document Copyright 2002-2004, Wizards of the Coast, Inc.; Authors Bill Slavicsek, Jeff Grubb, Rich Redman, Charles Ryan, Eric Cagle, David Noonan, Stan!, Christopher Perkins, Rodney Thompson, and JD Wiker, based on material by Jonathan Tweet, Monte Cook, Skip Williams, Richard Baker, Peter Adkison, Bruce R. Cordell, John Tynes, Andy Collins, and JD Wiker.
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And they are all quite grim and quite dark, seeing as the root of magic in DL is the Abyss.
