Book of shadows: Festering Blade

Festering Blade is cast on a weapon,  the weapon cracks and grows pustules that begin oozing necromantic foul. Immediately after casting 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 must make a constitution saving throw, on a failure they take 1D8  damage and it is also poisoned until the end of your next turn. on a success they take half the damage and is not poisoned.

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. Damage rolls increase by 1d8 at 11th level 2d8  and 17th level 3d8.