Broken sword

The caster targets a creature they can see. The targeted creature must make a constitution save. On a successful save nothing happens and the spells fails. On a failed save the target is weakened and has disadvantage on all attacks. Additionally the whenever the target successfully deals damage, they must roll [roll]1d4[/roll] and reduce the damage dealt by the amount rolled. 

When cast at 5th level increase the dice rolled to reduce damage dealt to [roll]1d6[/roll] . Change this to [roll]1d8[/roll] at 6th level and [roll]1d8[/roll] at 7th