True Wish

This spell allows you to wish for anything with no limits to what it is (except more wishes or other similar workarounds.)

However, it has a terrible cost. Once the spell is casted, the caster's max hp is cut in half permanently and nothing can undo it. The player can also no longer do death saves, so if you die, you die. Additionally, once the caster has casted the spell, they cannot ever cast it ever again.