Worldrot (9th-level necromancy) — an infection for all things

Casting Time: 1 action
Range: 300 feet (point)
Components: V, S, M (a pinch of powdered bone and a blackened seed worth 500 gp, consumed)
Duration: Concentration, up to 1 minute (see Seed option)

You speak a word older than language and hurl a mote of unmaking at a point you can see. A spreading corruption — a sickness of matter and life — blooms outward like a living shadow, rotting flesh, wood, stone and steel alike.

Effect

When you cast the spell, choose Immediate or Seed mode.

Immediate (default)

A spherical wave erupts centered on the chosen point:

• Area: 120-foot radius sphere.
• Initial Pulse: Each creature in the area must make a Constitution saving throw.
• On a failed save: the creature takes 10d10 necrotic + 10d10 acid damage and is Infected (see below).
• On a successful save: the creature takes half that damage and is Not Infected but is blighted (see below).
• Objects & Terrain: Nonmagical organic material (wood, crops, leather, rope) is instantly ruined. Nonmagical stone and metal take 50 points of structural damage (DM adjudicates structural HP); metal surfaces corrode and suffer disadvantage on checks to function (locks jam, weapons dull). Water sources within the area become undrinkable; soil within the area is poisoned and cannot support normal plant life for 1d12 years unless cleansed.
• Magic Items & Constructs: Magic items and constructs within the area must make a Constitution saving throw (same DC).
• Fail: A non-artifact magic item loses all charges and becomes inert for 24 hours (or until a Greater Restoration/Remove Curse/Wish). A construct takes 8d10 force + necrotic damage and is stunned for 1 round.
• Success: The item/construct resists and suffers no lasting effect but takes half of the structural corrosion effects.

After the initial pulse, while you maintain concentration, the rot continues to spread outward:

• Spread: At the start of each of your turns, the rotted area expands by 10 feet in radius (stacking each round while concentration continues) and any creature that enters or starts its turn inside the newly affected portion must make the Con save or suffer the infection effects described below.

Infected (condition)

A creature that is Infected suffers the following until cured:

• Ongoing Damage: At the start of each of its turns, the infected creature takes 8d8 necrotic damage and 4d8 acid damage.
• Attribute Decay: Immediately and permanently for the duration of the infection, the creature’s Strength, Dexterity, and Constitution scores each drop by 1d4 (minimum 1). This loss can only be restored by wish or a similar epic magic; lesser magic reduces the decay but does not fully restore it.
• Spread by Contact: If an infected creature deals melee damage to another creature, that creature must make a Con save or become infected as well.
• Healing Reversal: Any healing applied to an infected creature instead deals the same amount as radiant damage (healing becomes harmful) unless the healing is cast as a Remove Curse + Greater Restoration combination cast the same turn.
• Death by Rot: If an infected creature is reduced to 0 hit points by this infection, its body dissolves into black ichor and cannot be restored without Wish.

A successful Constitution saving throw at the end of a creature’s turn reduces the infection’s effects: on a success the creature takes no ongoing damage that round and no further ability score decay occurs; two successful saves (not necessarily consecutive) cure the infection entirely (though lost ability points remain unless restored by epic magic).

Blighted (failed save on pulse but not infected)

A creature that was blighted (saved vs initial pulse) takes no ongoing damage, but:

• Its natural healing is halved for 24 hours, and it has disadvantage on saving throws against poison, disease, and necrotic effects for 1d6 days.

Seed Option (permanent corruption)

If, when you cast, you choose Seed mode, the initial pulse forms a Corrupting Seed at the spell’s center — a black crystalline kernel of rot that continues to spread after you stop concentrating.

• Consequence: To create a Seed you must pay a cost: permanently reduce your Constitution score by 2 (this reduction cannot be restored except by wish or a deity).
• Seed Behavior: The Seed continues to expand outward by 20 feet per day on its own, infecting anything it reaches (use the infection rules above; creatures that pass through must save).
• Stopping the Seed: Only a Wish, a divine intervention, or performing a 7-day ritual at the Seed’s location (requiring 5 casters of 12th level+ and a holy/cleansing site) can destroy the Seed. Destroying the Seed ends the rot but leaves the landscape scarred for centuries.

Saving Throw DC & Scaling

• Spell save DC: 8 + your proficiency bonus + your spellcasting modifier.
• At Higher Spell Slots: This is a 9th-level spell; if your DM permits epic slots, every slot level above 9 increases each damage pool by +1d10 (initial) and adds +1d8 necrotic to ongoing per round damage.

Limits & Immunities

• Artifacts and true deities are immune unless the caster spends a soul of a lesser god during casting (DM call).
• Constructs and elementals are affected by the spell’s corrosive/material effects (metal corrodes, stone cracks) but may be able to resist infection via successful Con saves; undead are especially vulnerable — treat failures as automatically infected.
• Planar Boundaries: The spell affects the plane in which it is cast. If a creature is on another plane when the Seed spreads to that point, it is unaffected.

Ending & Removal

• Remove Curse/Greater Restoration can temporarily suppress symptoms but do not remove the Seed or undo permanent stat decay.
• Wish or a deity’s direct intervention is needed to fully cure infections, restore lost ability points caused by the infection, or eradicate a permanent Seed immediately.