True Hellfire

The frightening secret of Mephistopheles revealed, opening up an inferno from all Nine Hells, engulfing both body and soul. A secret known only to the highest members in the cult of Mephistopheles, this dangerous spell was hidden away for centuries, and should not see the light of day.

The caster chooses a spot they can see in range and rolls 1d10. Centered at that point, a towering inferno of dark fire erupts from that point in a 100 foot radius cylinder, 300 feet high. All creatures make a dexterity save. On a fail, they take 5d8 fire damage and 5d8 necrotic damage and one of the following effects, based on the layer as determined by the d10 roll. On a success they take half damage, from both the initial casting and the layer, and don't suffer from any additional effects, including having to roll saving throws:

• (1) Avernus (1st layer) - Fire and Brimstone erupts with the dark flames. All creatures take an additional 12d6 bludgeoning damage and 12d6 fire damage. All creature's bodies who die this way are immediately turned into a pool of blood.  
• (2) Dis (2nd Layer) - Threads of the oppressive layer swirl within the flames. All creatures take 12d8 psychic damage and make a wisdom saving throw. On a fail, the creature is frightened of the caster for 1 minute and gains 1 long-term madness that lasts indefinitely. These feelings are incredibly strong and can only be removed with a greater restoration spell or higher healing magic. All creature's bodies who die this way are left as husks of what the previous body was.
• (3) Minarus (3rd Layer) - Sickly ooze bubbles up along with the dark flames, coating the lower half of creatures.  All creatures take 6d8 poison and 6d8 acid damage and make a constitution saving throw. On a fail, they are poisoned for 1 hour and have their speed reduced by half for that time. This poison is incredibly strong and can only be removed with a greater restoration spell or higher healing magic. All creature's bodies who die this way turn into ooze and acid.
• (4) Phlegethos (4th Layer) - Fuming flames and ash erupt from the ground. All creatures take 12d8 fire damage and make a constitution saving throw. On a fail, they are blinded and deafened for 1 hour. This smoke and ash are incredibly strong and the blindness can only be removed with a greater restoration spell or higher healing magic. All creature's bodies who die this way turn into ash and smoke.
• (5) Stygia (5th Layer) - A flood of frigid water and ice explodes with the darkened flame. All creatures take 12d6 cold damage and 12d6 piercing damage. All creature's bodies who die this way are eviscerated by ice shards. 
• (6) Malbolge (6th Layer) - A geyser of lava erupts from the layer. All creatures take 5d10 bludgeoning damage and 5d10 fire damage, and makes a dexterity save. On a fail, one of their body parts is covered in lava briefly. Roll 1d4 and do the following effects, which can only be reversed/cured when the creature is healed by a regenerate or higher healing magic:
  
  • (1) Head - All ranged attacks and charisma checks (except for intimidation) are made at disadvantage.
  • (2) Legs - The maximum speed is reduced by half.
  • (3) Arms - All melee attacks and strength checks are made at disadvantage.
  • (4) Torso - The maximum health of the creature is permanently reduced by 2d10.
  • If the creature doesn't receive healing magic or cold damage within 1 round, they permanently loose that body part, except for the torso, where the creature also receives a permanent -2 to AC. If the creature loses it's head and can't survive without it, they instantly die. All creature's bodies who die this way melt into the lava.
• (7) Maladomini (7th Layer) - Toxic vapor and demonic Insects arise with the flame and infect everyone. All creatures take 6d8 poison damage and 6d8 piercing damage and makes a constitution saving throw. On a fail, they are poisoned for 1 hour. At the end of each poisoned creature's turn, they take 4d8 poison damage. They can attempt at the end of each turn to make a constitution saving throw, ending the effect on a success. This poison is incredibly strong and can only be removed with a greater restoration spell or higher healing magic. All creature's bodies who die this way are covered in boils and lesions. Any creature who touches a body that dies in this way makes a constitution save as trapped gas erupts from the body (DC 17). On a fail, they take 6d8 poison damage or half as much on a success. 
• (8) Cania (8th Layer) - A whirring blizzard rises with the dark flames. All creatures take 10d10 cold damage and make a constitution saving throw. On a fail, they are frozen in a block of ice for 1 minute. They are considered paralyzed during this time and have a speed of 0. At the end of each turn, the creature can make a strength check (DC 25) to attempt to break the ice. The ice has a HP of 50 and an AC of 15, and can only be damaged by bludgeoning or fire damage. All damage that exceeds the Ice's HP is carried over to the target. All creature's bodies who die this way stay frozen.
• (9) Nessus (9th Layer) - The fiendish howls of the Asomdeus and his kin beckon your soul as flames erupt all around. All creatures take 10d10 fire damage and must make a wisdom saving throw. On a success, the creature receives 3 points of exhaustion. On a fail, the creature dies. All creature's bodies who die this way turn into a Lemure, and can only be returned to their original body by a wish spell. 
• (10) The caster chooses the layer that the inferno erupts from (Must choose the layer before dexterity rolls occur)

If the spell is cast on a layer of hell, the caster can choose to forego the d10 roll and instead use the effect of the layer the caster is currently on. If the spell is cast on a Positive Energy Plane (Such as Elysium), roll a D20. On a 14 or below, the spell can not bypass the protection from plane and fizzles out, wasting the spell slot. On a 15-19, the spell proceeds but all creatures have advantage against the spell. On a 20, the spell proceeds as normal.

All creatures who die from this spell have their souls sent straight to the layer that was opened. Their soul can only be returned via a wish spell. Their soul can also be reincarnated, but the soul must be free from devil's control to succeed.