Void Blade

You manifest a weapon of negative energy and swing it. Make a melee spell attack against the target. On a hit, the target takes 1d8 psychic damage and must make a constitution saving throw or have its hit point maximum reduced by an amount equal to the damage taken on a fail.

You can make additional attacks with it as part of the same action when you reach higher levels: two attacks at 5th level, three attacks at 11th level, and four attacks at 17th level. You can direct the attacks at the same target or at different ones. Make a separate attack roll for each.