Invoke the Crimson Oath

Brandishing your weapon and shouting the final line of the Crimson Oath, you unleash a blast of destructive ruby energy. You must be wielding a melee weapon, and you perform this spell's somatic component by swinging the weapon in a downward arc. You deal normal melee damage for your weapon, including all appropriate bonuses, penalties, modifiers, and properties, to each creature in the spell's area; they must each attempt a basic Fortitude save. A creature that critically fails this save also suffers any additional effect you would normally inflict with your weapon on a critical hit; if the creature that critically fails its save is also immune to critical hits, it merely fails the save instead. You can convert all the physical damage from this spell into vitality damage against all undead creatures in the area.