The Rites of Astral Banishment

The rites of banishment are old and absolute. From the signing of the concordance and regarding that which holds together the fabric of reality, these rites are in place for the purpose of preventing a interplanar catastrophe. No one may ignore the demand for cosmic order, not even a god.

10th Level spells require extra-ordinary power to cast. In order to cast, a 9th level slot must be spent alongside the usage of a relic called a divine spike.

As part of the spell, a handful of ashes of a god must be cast into the air in the direction of the entity (which must be within 120ft). In addition, the words: "Back into the shadow of whence you came, to where sun doth not set and mortal eye may not see until death's call. Return to the hells, to immortal imprisonment, and bleakness of your wretched desires. And never come back." must be spoken aloud so that the target may hear. The spell begins being cast as an action on the user's turn. They must concentrate on the spell for 1 round, and are [condition]Incapacitated[/spell] while doing so.

If this is done, it must make a wisdom, charisma, and intelligence saving throw. If the target is not a god, it need only fail one for it to take effect. If the target is a god, all three must be failed for the spell to take effect as described below.

If the target is native to the plane of existence you're on and not a god, you banish the target to the nine hells, the abyss, or hades, never to return. The exact location is for the DM to decide. The target remains there until the banishment is broken with more powerful magic, or a loophole is found within the rites of banishment (which are extensive and impossible to fully comprehend).

If the target is native to a different plane of existence than the one you're on, or is a deity, the target is banished instead to any of the outer planes, whichever is capable to house the entity and is not the plane that the target is currently on. The exact location is for the DM to decide.

The usage of this spell is physically taxing for a mortal to cast. When it is cast, and succeeds, it can never be cast again by that creature.