Concentrate (joke spell)

You call upon your minds inner well to focus on this one particular spell. Immediately when you cast this spell, you begin to concentrate on it. If you are hit while concentrating on this spell, you must make a Constitution saving throw (DC 10 or half the damage you took, whichever is higher). On a failed save, you break concentration and the spell ends. On a success, your concentration maintains, and the spell is not broken. If a different spell that requires concentration is cast while concentrating on this spell, the concentration for this spell is immediately broken, and is instead replaced by the other spell.

The GM might also call for a Constitution save if something is ruled as disruptive (examples: a loud noise, a ship suddenly being thrown to the side, or harsh winds). The DC for this check is determined by the GM, though the rest of the rulings are the same as listed above.