Corpse Slayer

From Explorer's Guide to Wildemount, page 266.

Description
Weapon (any), rare (requires attunement).

You gain a +1 bonus to attack and damage rolls made using this magic weapon.

When you hit an undead creature with an attack using this weapon, the attack deals an extra 1d8 of the weapon's type, and the creature has disadvantage on saving throws against effects that turn undead until the start of your next turn.