Stormbringer

+3 magic intelligent greatsword
Only non-lawful characters may attune to it.
When kill a non-construct with this, it eats the
creature's soul - Prevents the creature from being
revived except by Wish, then grants you
temporary HP equal to victim's max HP for 24
hrs. During that time you get Advantage on attack
rolls, saving throws and skill checks if holding
Stormbringer. Killing multiple victims doesn't
stack the bonus, but resets the temp HP and clock.