Sword of Feast and Famine

This awe-inspiring longsword is split down the middle, resulting in two separate blades, placed side-by-side. One blade shimmers with a sickly-green light, while the other seems to gather the shadows about it. You have a +2 bonus to attack and damage rolls made with this weapon, attacks made with this weapon deal an additional 1d8 necrotic and 1d8 poison damage, and while wielding it, you have immunity to necrotic and poison damage. When a creature takes damage from an attack made with this weapon, it must make a DC 20 Constitution saving throw. On a failed save, you can either choose to regain a number of hit points equal to the damage dealt or cause the target’s maximum hit points to be reduced by an amount equal to the damage dealt. If a creature’s maximum hit points are reduced to 0 in this way, it dies automatically. This reduction lasts until the end of the target’s next long rest.