Poisonous rain covers and pools on the ground in a 10-foot square centered on a point within range and turns it into difficult terrain for the duration.   When the rain appears, each creature standing in its area must succeed on a Constitution saving throw or become poisoned. A creature that enters the area for the first time on a turn must also succeed on a Constitution saving throw or become poisoned. A poisoned creature can repeat this save at the end of their turns, ending the condition on a success.