Apocalypse

You spend one to five minutes casting a ritual using a powerful skulls as the catalyst. You choose a point within range, and in a 100 foot cube centered on the point. All creatures who start their turn or when they first enter the area, must succeed on a Constitution saving throw or take 3d10 necrotic damage, are poisoned for 1 minute, gain 1 level of exhaustion, and become vulnerable to necrotic damage. A creature that succeeds on its saving throw, only takes half damage, and suffers no additional affects.

Any humanoid that dies while within the area, rises again as a zombie or skeleton, immediately becoming hostile to any creature near it. Additionally, any humanoid that is killed by a zombie or skeleton created by this spell, even outside the spells area, rises as a zombie or skeleton after 24 hours, unless they are brought back to life or their body is destroyed.

For each additional minute you spend casting this spell, the area is increased by 100 feet, up to a maximum of 500 feet.

You can keep concentration on this spell beyond its normal time limit by sacrificing your life force or the life force of others to fuel it. You or one creature within 30 feet of you must succeed on a Constitution saving throw or take 3d10 necrotic damage and suffer 1 level of exhaustion. On a success the creature still takes 3d10 damage, however, does not suffer 1 level of exhaustion. If the creature is unwilling and succeeds on their saving throw, you instead take the damage and suffer a level of exhaustion. Each time you sacrifice life to fuel the spell in this way, the duration of the spell increases by 1 hour. Should you do so 100 times, the spell becomes permanent and no longer requires concentration.

This spell does not affect undead, and celestials have advantage on their saving throws against it.