Each plane is inhabited, and the nature of the planes and the being there has combined to impact them in different ways. Some are exceedingly powerful, potent, and dangerous. Others are considered weak and subject to the powers of those above them according to the nature of the world there.
There is little back and forth travel between the Planes and the Prime, except among the inner planes of the Mortal Plane. Each plane has its own set of peoples and its own inner planes, and those in turn are also thought to be easier to pass through. To cross between the greater planes, the Seven of them, one must put forth enormous energy and effort, and there is always risk. While you could get lucky on a general summoning and bring across some nameless beast from a different plane, should you bring across a sentient being you should always be extra careful. Even more so if you seek to bargain or command them.
Most summoning is done through rituals, with engraved spaces, though on occasion some coven will try to do it without a fixed or precise basis, and the tales that accompany that are horrific.
These are sentient beings, and they are not people, and they are dangerous and dislike being subject to the will of others. A small error in crafting a summoning can result in them being called, but then them taking the summoner back to serve them as a slave.
Worse: once they have been summoned by you, they can then in turn summon you to them once released.
Ritual Summoning is a special form of Ritual Magic. It is Advanced in its complexity and exists across all Affinities. It has a massive mana cost, takes 11 hours to cast, followed by an hour to solidify, and has complex, specific material components and set up prior to the casting that must be exact and match the being that is summoned.
An open summoning can be performed, but the results are unpredictable, and so typically people will focus specifically on the summoning of known being, whose powers and abilities are in line with what is desired (summoning a human from another plane is just going to give you a human).
On occasion, someone will decide that they have the power and privilege and place to summon another being from one of the planes. This typically goes poorly, which is why we have Spectres, Wraiths, Beholders, Trolls, Yuma, Wisps, Shades, Hypnarachs, Angels, Malakim, Valkyries, Devils, Demons, Yogs, Hags, Khrysos, Lepras, Wrights, Ghouls, Ghasts, and assorted undead. To name a few.
Ritual Summonings are comparatively easy to perform, extremely difficult to prepare for, and usually have a bad result. The beings of the many different Planes are still sentient beings, and often deeply resent when someone yanks them out of their lives and hauls them into another world and then demands they act essentially as slaves for them.
A poorly conducted ritual can summon some beast from the other planes that might be terrified or enraged, that will not have the natural capacity to support itself, may not even be able to eat anything here. Meanwhile some Lord or Power could be summoned but doing so then places the summoner in the position of having to ensure their own safety.
A Summoning Ritual involves an inscribed ritual cipher with a greater and specific managram, with the inner diameter about six feet across. It can be larger or smaller, and the size matters as the being will be contained within that inner area at first unless it is too small to do so, in which case it will break the circle and free the being.
Ritual spaces are set up with salt, silver, iron, and blood. There are always these four things involved – salt forms the glyphs and works with the silver which must be poured into the cipher channels uniformly and evenly. Blood must join and be used to set the magrams, and iron must be mixed with that blood for some parts of the sigil, whereas silver must be mixed for others.
All Ritual Summoning involves an Offering. Offerings are specific to the plane and needs of the summoned being. Summoning a human from some other world may only require something they desperately want, whereas summoning a demon may create a problem in how you provide the emotional power they desire.
Most commonly, the offering ends up being the death, pain, terror, and flesh of some living being, because people seem to always try to summon something infernal or necrotic. All offerings are consumed, in total, regardless, as a part of the spell. So even for something Radiant or Celestial, where the offering may be a newborn for innocence, the offering is destroyed. There is no Ritual Summoning that does not involve an offering, and so there are likely to be few Ritual Summoning events that are not foul and evil and cruel, even when the goal is something benign or beneficial.
Summoned Beings are confined to the inner circle. Breaking that inner circle can free them – disturbing the salt line, or marring a glyph or rune, or even the slightest imperfection in the silver channel can break the ring. Sometimes it is enough to stop it before anything is summoned, but other times it may work, and the being may not act immediately.
Summoned beings must be done so by name, or the ritual could bring across any denizen of that plane. Many historically summoned beings have worked to ensure that their names are available, and they will often have designs on those who fail, including slavery and taking the summoner back to their plane with them as a slave. This can be exceedingly bad, as magic on the other planes is not the same as magic here, often meaning the only way they can return themselves is if they are summoned.
A summoning ritual can be performed by a single person. The Rites are often found, with the names of certain individuals whose summoning may have been successful and beneficial to the mage, in scrolls, tomes, and even carvings. The Mana cost of a ritual summoning is frightening. Because of this, often large groups will form to share the mana among them to achieve the amount needed.
A summoning ritual must be performed without break, and once complete takes an hour to enable the being to appear during which the Ritualist cannot do anything but concentrate.
If everything else is done properly, a summoned being will be stuck within the circle, and not be able to be freed until the Ritualist releases them. Summoning is often done for a purpose, a goal, and summoners often invoke a geas of some sort, that enforces any agreements or bargains made. Without that, however, there is little holding the summoned being in thrall.
They are all essentially bound up here, into this form of spellcraft, and while not illegal under imperial edict, they are under Akadian Principles, and they apparently really anger Chicory and her friends.
Very few will perform a summoning ritual, and even fewer will perform one twice.