Ceremonial Magic

The caster can take a number of spells that they have prepared and cast them together. The caster can only use spells that either has a timed or concentration duration and cast them as a ceremony. The spells will all work together and gain the concentration duration regardless of if they have a fixed duration.

Any spell with an instantaneous effect such as a summoning or damage dealing can be part of a ceremony. However, the element it forms ends once the preparation phase is over.

The ceremony takes 10 minutes plus the total level of spells, and the caster must be able to concentrate throughout the preparation or all of the spells are lost.
If the spells require verbal or somatic components then the caster must be free to move, chant and make the appropriate symbols throughout the casting.

When the preparation time is complete the spells will take effect together and continue to operate while the caster concentrates. The caster must make a successful save on their appropriate spell save ability or lose the spells. If the caster is interrupted while preparing then they will take 1d6 psychic damage per total level of the spells being cast.
The caster must also make a fresh save every 10 minutes or the ceremony collapses.

The caster can have help while casting the ceremony (other people praying or chanting), in this case, the caster and their helpers make a group save 'at advantage'. If the group is interrupted all present take the psychic damage.

If the spells being cast do not have material components then the caster can gain an advantage on the save by using items or incense which the spells will consume. The value of the items must be 1gp per spell level. (For instance, food that may make up a good meal could be used as an offering).

Advantage on the save can be gained if chalks, powders or other marking materials are used to indicate an area within which the spells will operate then they will cost 1gp per total spell level and will be drawn around those involved in the ceremony. If a boundary exists and the spells involved have an area effect then the spell effects are confined to the bonded area.
Disturbing the markings will break the concentration.