Blasphemous Embodiment

A blasphemous and forbidden ritual once sealed away by Ioun, this spell allows the caster to draw the essence of a god into a mortal body which can then be slain, killing the god. Once you have the components prepared, the caster must maintain their concentration and perform the unholy incantation for twenty four hours without rest. The deity being summoned knows the spell is being cast on them, but not where the spells is being cast. They may immediately send servants to locate and stop the ritual before it is completed.

When the ritual has reached its completion, the caster must touch a willing creature. That creature's soul is destroyed and is replaced with the essence of the god the caster has chosen to embody. The body transforms to take on the aspects of the deity that now inhabits it, and the stats change accordingly. However the new body is mortal and shares the limitations of mortal creatures. It can have no more than 33d20 + 330 hit points and an Armor Class no greater than 25.

If the caster touches an unwilling creature, you must first make an unarmed attack to hit the creature; then that creature must make a Charisma saving throw vs your spell save DC. On a succesful save, the target takes 12d12 + 20 psychic damage, you take half as much psychic damage, and the spell is expended. On a failed saving throw, the target's soul is destroyed and the god is incarnated as normal.