Ritual of Summoning

The Ritual of Summoning is the process formerly used by powerful mages at The Amber Temple to summon Dark Powers prior to weakening and imprisoning them. This information was curated by your friendly neighbourhood lich.

Trapping a Dark Power

A Dark Power cannot, so far as we’ve been able to ascertain, ever be truly destroyed or contained. It can, however, be weakened, and that has been part of the core mission of the Amber Temple since first it was founded.
We have made extensive use of amber and iron in the construction of this temple, and it is amber most of all that we have found useful in weakening individual Dark Powers, subduing their ability to run rampant across the realms, ensuring that they remain only truly strong within the Domains of Dread themselves.
The ritual described herein should only be undertaken by the most accomplished of mages and priests. To weaken a Dark Power, you must first summon that Dark Power, and such an encounter is not something easily survived. You will want not only a minimum of three accomplished magic casters, but many guardians ready to protect them — and to die in the process, if necessary.

Summoning the Dark Power

This ritual requires at least three casters maintaining continuous, uninterrupted ten-minute casting. The materials for the ritual to entrap the Dark Power should also be on hand, as both rituals should be done back to back to minimise destruction.
One must have the name of the Dark Power one is looking to summon, and some characteristics of the Dark Power.
Ideally, all casters should be either mages or those with divine magic, with adequate knowledge of the immensity of the power they are about to face. The greater the magical ability of the casters, the better the chance these rituals have of succeeding, though casters only capable of up to 5th-level spells have successfully undertaken this process, and even casters only capable of 3rd-level magic have participated. It is highly inadvisable, however, to undertake this ritual or the one that follows without at least one caster capable of 7th-level spells or greater magic.
Though more than three casters can participate in this ritual (and having more will certainly bolster the spell’s chance of success), at least three must maintain concentration on the ritual for the entirety of the casting time. If at any point fewer than three casters are actively concentrating on the ritual, the ritual will fail, consuming the magical energy required for the casting, and must begin again.
If at any point the caster leading the ritual loses focus, the ritual will fail, consuming the magical energy and requiring a fresh start.
If the Dark Power is being summoned in a hostile environment, it is strongly recommended that guardians be present to protect the casters and prevent them from being distracted from their task. If at all possible, the ritual should be undertaken under circumstances where there is no expectation of interference.
The lead caster must call to the Dark Power by name, challenging it to appear. The caster must call upon their knowledge of the Power, showing that it is worthy of an audience. They must interweave their request with words of power to help summon the Power, and to bind it to remain in place once summoned.
The Dark Power cannot be summoned if it has an active, fully realised bond with one of its champions. All bonds must be severed, either through rejection of the Dark Power or death of the champion, in order for this ritual to succeed.

In Mechanical Terms…

At least three people capable of casting third-level spells or higher are needed to perform this ritual.
Other casters with lower levels of magic can attempt to participate, though you have no idea whether or not they’d help or hinder; to be fair, these are the writings of high-level mages, so there may be bias in the guidelines they’ve left behind.
Ideally, at least one caster capable of casting seventh-level spells or higher should lead the ritual, choosing what level of spell slot the ritual will consume.
For ten minutes, at least three of the casters must maintain concentration on the ritual.
If any of the casters take damage or are otherwise subjected to distracting effects over the course of the ritual, they must make Concentration checks, as when maintaining Concentration on a spell.
The lead caster will have a bonus on these Concentration checks equal to the number of other casters participating in the ritual (minimum +2).
While maintaining Concentration on the ritual, casters cannot use actions, bonus actions, or reactions. If they do so, they break Concentration for that turn and must begin again on the next round.
Casters other than the lead caster can speak without breaking Concentration, but prolonged or especially distracting conversation may impose disadvantage on the next Concentration check.
If at any point fewer than three casters are maintaining Concentration, or if the lead caster loses Concentration, the spell slot is consumed and the ritual fails. It must begin again from the beginning, with a new spell slot chosen.
Though I won’t give you the exact DCs involved, in the following ritual, you will be given advantages based off the following factors:

• The number of casters maintaining Concentration at the end of the ritual
• If at least two casters maintain Concentration continuously alongside the lead caster for the duration of the ritual
• The level of the spell slot used to conduct the ritual

Ri-An and Bodaway, with their Arcana proficiency, would be able to decipher that all of these things would be good/helpful