The River King can breathe air and water.

If the River King fails a saving throw, he can choose to succeed instead.

The River King’s weapon attacks are magical and do an extra 10 (3d6) lightning damage (included below).

the region containing the River King’s lair is warped by its magic, which creates one or more of the following effects:

• The current of rivers and streams within 6 miles of the lair becomes strong and erratic. Creatures without a swim speed who start their turns in running water must succeed on a DC 15 Strength (Athletics) check or be swept 60 feet downriver.

• Lakes, ponds, rivers, and streams within 6 miles of the lair teem with fish and other wildlife.

• Rain and thunderstorms are common within 6 miles of the lair, and often build to torrential downpours that create heavy obscurement and cause waterways to overflow their banks.

if the River King dies, conditions in the area surrounding the lair return to normal over the course of 1d10 days.

on initiative count 20 (losing initiative ties), the River King takes a lair action to cause one of the following effects; the River King can’t use the same effect two rounds in a row:

• The fey river swells and rushes over the land, or the walls of the Hall buckle and allow the torrent in. The River King chooses a 10-foot-wide path up to 60 feet long. Each creature in the path of the water must make a DC 15 Strength saving throw. Creatures that fail the save are swept 20 feet down the path of the water and take 9 (2d8) bludgeoning damage.

• The River King targets a creature he can see within 60 feet. That creature’s mouth and throat fill with river water. The creature must make a DC 15 Constitution saving throw. On a success, the creature manages to hold its breath, but on a failure, it begins to suffocate. A suffocating but conscious creature repeats the saving throw at the end of its turn, ending the effect on itself on a success. Another creature within 5 feet can use an action to make a DC 15 Wisdom (Medicine) check. On a success, the suffocating creature coughs up the water and the effect ends. Otherwise the effect lasts until the River King uses this action again or dies.

• The River King targets a creature he can see within 120 feet. His commanding presence overwhelms the creature, who must make a DC 15 Charisma saving throw. On a failure, the creature is charmed by the River King until initiative count 20 on the following round.