Colonic Confusion

A creature of your choice that you can see within range looses control of their colon and falls into fits of diarrhea and vommitting if this spell affects it. The target must succeed on a Constitution saving throw or fall prone, becoming incapacitated and unable to stand up for the duration of the diarrhea fit. A creature with a Constitution score of 18 or higher cannot be affected by this spell.

At the end of each of its turns, and each time it takes damage, the target can make another saving throw. The target has advantage on the saving throw if it's triggered by damage. On a success, the spell ends.