Apotheosis of Karsus

You create a tear through the weave and you draw a sliver of divinity from a deity or an entity that is willing or unwilling but either way they are aware of such action.  As part of casting, this spell you reduce your maximum hit points by half (rounded down) and this reduction remains until the spell ends. During this time the divine power that surge through you granting god like mastery of arcane. Any spell that you cast that is of 6 level or lower doesn’t cost a spell slot, cannot be resisted or countered and you can’t lose concentration to maintain spells.

Once the spell ends you immediately gain 3 points of exhaustion (cannot be resisted) which can only be removed by taking long rests.