Thorne's Blade of Ragmotholl

You brandish the weapon used in the spell’s casting and make a melee attack with it against one creature within 5 feet of you. On a hit, the target suffers the weapon attack’s normal effects and then becomes sheathed in shadowy tendrils until the start of your next turn. If the target ends their turn in the same space they were in when this spell was cast, the target takes 1d8 necrotic damage, and the spell ends. The caster of this spell heals for half of all necrotic damage dealt by this spell.

This spell’s damage increases when you reach certain levels. At 5th level, the melee attack deals an extra 1d8 necrotic damage to the target on a hit, and the damage the target takes for ending their to 2d8. Both damage rolls increase by 1d8 at 11th level (2d8 and 3d8) and again at 17th level (3d8 and 4d8).