Metabot's Manual of Magical Maneuvers

Siphoning Strike

0-level (Cantrip) Necromancy

As part of the action used to cast this spell, you must make a melee attack with a melee weapon against one creature within the spell's range, otherwise the spell fails. On a hit, the target suffers the attack's normal effects and if you reduce a hostile creature to 0 hit points, you siphon off a bit of its soul. Your next attack with that weapon before the end of your next turn deals additional necrotic damage equal to your spellcasting ability modifier.
At higher levels: The spell's damage increases when you reach higher levels. At 5th level, the melee attack deals an extra 1d8 necrotic damage to the target, and the necrotic damage on the next attack before the end of your next turn increases to 1d8 + your spellcasting ability modifier. Both damage rolls increase by 1d8 at 11th level and 17th level.