A seething beam of pure negative energy flashes out from you in a 10-foot-wide line that extends as far as you can see. The beam destroys all nonliving material it comes into contact with, and can burn through 10 feet of material per second it is focused on a point. Each creature in the line must make a Charisma saving throw. Good-aligned creatures have disadvantage on this saving throw. On a successful save, a creature takes 8d12 necrotic damage and isn't otherwise affected. On a failed save, it takes 12d12 necrotic damage and is banished to the Negative Plane. Each round it remains in the Negative Plane, it can make a DC 25 Charisma check to escape. On a failure or if a check is not attempted, the creature takes another 8d12 necrotic damage. On a success, it escapes the Negative Plane and reappears in the space it occupied when it was targeted by the spell.
You can move the endpoint of the beam up to 300 feet as your action on any turn until the spell ends. The effects of the spell trigger on any creature or nonliving material the beam or the endpoint comes into contact with as it moves. If you are not in combat/targeting creatures with this spell, you can move the endpoint of the beam at will.
For the duration, an aura of enveloping darkness radiates from you. It turns all bright light within 30 feet of you into dim light and extinguishes all dim light within 60 feet of you. This darkness is magical. It cannot be dispelled while this spell lasts, and creatures with darkvision or truesight cannot see through it.
This spell is not meant to be used by those not possessed with extraordinary power. If you are not the host of an Elder Evil, you die after casting this spell and cannot be revived. If you are the host of an Elder Evil, you instead take necrotic damage enough to drop you to one hit point. This can be prevented by casting the spell as part of a group. Each member of the group must be of a level and class such that could cast this spell. The group takes 10,000 necrotic damage divided evenly among its members. For each level (of the type specified above) of any member of the group that is higher than necessary to cast this spell, subtract 10 damage from this total.
Effects of this spell or its Negative Plane function cannot be reduced or avoided in any way other than saving against it or successfully escaping the Negative Plane, and hit points lost to this spell or the Negative Plane function cannot be regained in any way other than divine intervention (heals up to half of the damage), the intervention of an elder evil (heals up to half the damage, or all of the damage if the evil is the one bestowing the ability to cast the spell, who can also waive damage dealt to the caster), or the wish spell (heals up to 10 of the damage).