D&D Ritual Casting

Ritual magic is a commonly used plot point in fantasy stories. Circles of witches gathering around a cauldron, a
cloister of priests performing a sacrifice, or a college of wizards banding together to perform a powerful spell.
The general idea behind ritual magic is to allow spellcasters to cast spells they could not normally cast at their
level - obviously, the rules must be strict in controlling this, or the game is quickly broken by high-level spells
such as Wish perpetually fuelling themselves in rituals.

The steps to performing a ritual:

1. Choose the Spell

This step is very simple - determine the spell the caster wishes to perform the ritual to cast. The spell must be
known to the caster, through a spellbook, scroll, or innately. Note that casters who do not normally cast spells from
spellbooks may still use a spellbook to perform a ritual, just as they would be able to use a scroll.

2. Determine Costs

The cost of a ritual is based on the required level to cast the spell, minus the caster's own level. To perform the
ritual in one hour, the cost is equal to this difference squared, times 1000gp. For example, if Red, a 7th level
Sorceress, wants to cast Scry, a 4th level spell, it would cost 1000gp in materials as an 8th level Sorcerer can cast
Scry. If she wanted to cast Control Weather instead, it would cost 49000gp to do in an hour, because only a 14th level
or higher sorcerer can cast Control Weather.

3. Reduce Costs

Obviously, the cost of very large rituals is extremely high. There are ways to reduce these costs, however. The first
is by using a longer ritual. For every doubling of the ritual's length, one caster level is 'free'. So if Red wished
to cast Scry with no cost, it would take two hours. If she wished to cast Control Weather with no cost, it would take
128 hours, or a bit more than 5 whole days. Note that this allows for no breaks in the ritual - no food, water, or
rest. She would have to magically sustain herself while performing the ritual, or likely perish from dehydration or
exhaustion.

A ritual need not be performed alone, however - a magician may have assistants. Assistants can work in two ways: they
can shorten the ritual time, or they can allow the main practitioner of the ritual to rest during the rite.

An assistant whose caster level is at least one-half the leading magician's reduces the time for the ritual by half,
provided the assistant also knows the spell. An assistant whose level is less, or who does not have knowledge of
the spell, provides only half the benefit - in the worst case, the time is reduced by one-eighth.

Multiple assistants' benefits stack, but not completely. The benefit of each assistant is halved after the first - so
the optimal situations tend to be a large number of inexperienced acolytes, or a master magician and a single skilled
apprentice. For example, if Red wanted to cast Control Weather with a 4th level Sorcerer and a 2nd level Sorcerer,
who both had the same knowledge of the spell (likely a book), the first assistant would halve the time to 64 hours,
then the second assistant would reduce it by one-eighth (halved for being the second assistant, halved again for
not having enough caster levels). The final casting time would be 56 hours - slightly less than two and a half days.
This is still very tiring.

The other option is to have an assistant take over the ritual while the main magician rests. An assistant doing this
will make one-half the progress of the master if the assistant is at least half the master's caster level and knows
the spell in question. Otherwise the assistant will make no progress, but by continuing the rite can 'suspend' the
ritual until the master returns.

Another method of reducing the cost of a spell is with a sacrifice. A sacrifice provides the same benefit as an
apprentice with a caster level equal to the caster's hit dice, who does not know the spell in question (reducing by
one quarter). Multiple sacrifices contribute like multiple assistants, and progress separately (so two assistants and
a sacrifice would not reduce the potency of the sacrifice). Different rituals may require different requirements for
the sacrifice - consult the DM. Because for Arcane magic, a sacrifice mostly entails using the creature's body and
soul as a source of raw power, this is always an Evil act. For Divine rituals, however, sacrifice is not always an Evil
act - sacrificing an animal, or an Evil creature may be part of a Good ritual, depending on the deity in question.
Druidic rituals care not for good or evil, and sacrificing sentient creatures is more common than sacrificing animals.

4. Cast the Spell

Ritual spells are never prepared, or retained. They are cast immediately upon completion of the ritual. The ritual may
be suspended as above by the magicians in order to wait for a crucial moment (phase of the moon, or presence of
the target, etc). They must not abandon the ritual.