Evil rituals will show up in any fantasy themed adventure game from time to time. Maybe some cultists are trying to summon their lovecraftian god, or perhaps they’re attempting to transform their high priest into a huge monster. Either way, the GM will need to produce a ritual for the players to try and stop.
The way I see it, each ritual has three essential elements: preparation, preamble, and catalyst. There are also a fourth element which is optional: Timing. While not all rituals will require it, sometimes they will only work if they are performed at a certain time, such as during a full moon, when the planets align, or on the anniversary of an important event.
The preparation for a ritual may involve gathering the necessary components, or learning an ancient incantation which must be spoken for the ritual to succeed. Strictly speaking the preparatory phase is not part of the ritual proper, but it is vital to the success of the ritual. Additionally, the preparation phase is frequently how the players will learn about an upcoming evil ritual, and it serves as the best opportunity to nip the villain’s evil plans in the bud.
When the time for the ritual actually arrives, it begins with the preamble, which can go on for a long while The length serves two purposes. First, it lends greater weight to the upcoming catalyst portion of the ritual. This buildup is essential, because nothing of great importance is accomplished quickly. Secondly, the duration of the preamble is the only period of time when the ritual has begun, but has not yet resulted in anything really bad happening. This gives time for the players to act to stop the ritual, which can be exciting.
The final phase of a ritual is the catalyst. This is short, generally a single action which will trigger whatever end result the ritual was intended to produce. If the cultists are summoning their evil god, then the moment the catalyst action is performed, then the portal will open, and the dark god will step through it.
Below are ideas for the preamble and catalyst of an evil ritual. Mix and match as you choose! A ritual could even combine multiple preambles together, as many real world religious ceremonies do. Additionally, almost any of these rituals could require a certain number of people to participate.
Reading from an important book: Sacred texts have great power, particularly in religious ceremonies. But an arcane ceremony could also include this trope. Perhaps a wizard summoning a demon must read that demon’s 20-page true name in its entirety before the demon will respond.
Singing/Chanting: While it may sound a little silly to sing at a ritual, this is actually quite common in many real world rituals. Imagine, for example, most christian ceremonies. They include a great deal of singing. Many Native American rituals do as well.
Praying: Normally a very particular prayer would need to be said, one which glorifies the being who will choose to grant, or not grant, the ritual’s end result.
Telling a story, giving a speech: Storytelling has long been an important part of human culture. To use a real world example, imagine that those performing the ritual wished to ask Heracles to bestow his strength upon them for an upcoming battle. Part of that ritual may involve a recitation of the 12 labors of Heracles.
Torture: The victim here could either be willing or unwilling, and the torture need not end in death. Perhaps the victim of the torture will even end up being the beneficiary of the ritual’s gifts. The god must see that the person they are empowering is willing to endure suffering.
Creating An Appropriate Environment: If done ritualistically (especially in combination with one of the other Preamble elements above) this could be part of the ritual itself, rather than part of the ritual’s preparation. Imagine, for example, a dozen cultists painting arcane symbols on their bodies, while a high priest chants the words of a magic spell.
Sacrifice: The numerous ways in which a victim could be sacrificed could be a post unto itself. Nearly any way a person could be killed might be used in an evil ritual. I, personally, would avoid the cliche of tying the person to an altar and stabbing them with a ceremonial knife. Be creative, and make the catalyst match the theme. If the cultists are summoning a tidal wave to wipe out a city, then drown the victim. If they’re summoning the god of snakes, then have them kill the victim with poison snakes.
Sex: This one works best if the result of the evil ritual is being applied to the child which is being conceived at the time. By having sex under the full moon while a dozen cultists chant prayers to The God of Horribleness, the child will be born as the Avatar of Horribleness.
Inducting New Members: Evil religions make a big to-do out of bringing new members into the fold. At the conclusion of an evil ritual, a new member could be baptized (whatever that means for the particular religion), thus increasing the number of the evil god’s followers.
Desecration of a Holy Object: Destroying a sacred artifact of great power, or otherwise desecrating something which radiates holy magic is sure to please any evil god, and weaken the followers of good.
Cannibalism: It’s difficult to imagine an act more evil than this. Once a person eats another, there can be no redemption for them. So it makes the perfect centerpiece to an evil ritual.