Curse of Wheaton

You magically restrict the amount of damage a chosen target can make. The chosen target must succeed on a charisma saving throw against the spellcaster's spell DC, or every damage roll the chosen target makes will automatically be the minimum amount of damage. 

This spell lasts until either the next long rest or until the chosen target's player rolls a Natural 20 on an attack, saving throw, or skill check. It may also be removed by Greater Restoration or Remove Curse.

At higher levels, the duration extends by one day per every 2 levels above 4th level.