The End

This spell is intended to end the world through a zombie apocalypse.

You attempt to touch and curse a living creature (not a construct, ooze, plant or undead). Make a melee spell attack. On success you deal 5d12 necrotic damage. If they survive they must succeed on a Constitution saving throw or become cursed by this spell. If they die they are cursed immediately and considered to have died while cursed (see below).

While cursed the target gains 1 level of exhaustion and a number of 'curse points' equal to your spellcasting ability modifier (minimum 1 point). The level of exhaustion cannot be removed by rests or magic of any kind while cursed. When the target next completes a long rest they gain more curse points - again equal to your spellcasting ability modifier (minimum 1 point). Once the target has accumulated enough curse points to equal or exceed their Constitution score and next complete a long rest - they die.

When a cursed target dies their soul is trapped within the corpse preventing any form of resurrection and when night next falls they rise as undead at full hit points, if they still have a body. The target, as undead, retain their stats except for the following changes:

• Their Dexterity, Intelligence, Wisdom and Charisma scores receive a -2 penalty as do their maximums but will not reduce any score or maximum below 2.
• Their Strength and Constitution scores increase by +4 as do their maximums.
• They gain proficiency with Constitution saving throws if they did not already have it.
• They become immune to poison damage and the poisoned condition.
• All exhaustion levels are removed and they become immune to exhaustion.
• They gain resistance to Necrotic damage but also gain vulnerability to Radiant damage.
• They no longer need to eat, drink or sleep. They cannot be put to sleep by any magical means.
• They gain Undead Fortitude trait: If damage reduces the target to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the target drops to 1 hit point instead.
• They gain Blindsight to 30 ft and Darkvision to 60 ft if they do not already have these.
• They gain the trait Deathbound: If the target ends any turn at 0 hit points they die but the soul remains trapped inside and the target remains cursed.
• They gain the trait Regeneration: At the start of their turn the target regains 10 hit points. If the target was dead they awaken again as undead under this curse. Only complete destruction of the body or brain prevents this.
• They gain a Bite attack. This is a melee attack with a reach of 5 ft that is based on their Strength. It deals 1d4 piercing damage plus 1d6 necrotic damage. If the recipient of this bite is a living creature (not a construct, ooze, plant or undead) then they must make a Constitution saving throw against your Spell Save DC and if they fail they become cursed by this spell as if you had cursed them with it.
• They become charmed by you and this cannot be broken or removed by any means.
• They are compelled to attack any living creature they see and try to bite and spread the curse where possible but can choose the method of how to accomplish this since they retain awareness and intelligence (albeit with penalty) and all their skills and memories. However, they are not truly themselves, they are driven by the curse, and this changes their personality and alignment to Chaotic Evil. The "real" them is a soul trapped inside, probably watching in horror from within at what this evil version of themselves is doing.

A cursed target can only have the curse removed by a Remove Curse or Greater Restoration spell cast as a 9th level spell or with a Wish spell. If the target had become undead, however, they cannot be cured of this curse by these spells. A target (living or undead) is also cured of this curse if their bodies are completely destroyed, freeing their souls.

If after casting this spell all cursed targets become uncursed then you become cursed yourself and then you immediately die. If you are ever freed from the curse then your body, if still around,  disintegrates into dust and your soul is destroyed forever unable to ever be resurrected. You tried to end the world and failed so oblivion is your reward.