Charun's Tainted Grimoire

This weathered and cursed grimoire is bound in dark leather and emanates a faint, eerie glow. When you attune to the Tainted Grimoire, you gain the ability to cast the Animate Dead spell once per day without expending a spell slot. Additionally, whenever you cast a necromancy spell of 1st level or higher, you can choose to regain hit points equal to half the level of the spell cast (rounded down). However, the magic within the grimoire is tainted; every time you use this ability, you must succeed on a DC 13 Constitution saving throw or suffer one level of exhaustion as the dark energies siphon your strength.