Multiattack

The shadow river lord makes two greenfire staff or two shadowfrost bolt attacks. If two attacks hit the same target, the target must make a DC 16 Constitution saving throw or be blinded until the end of its next turn.

Greenfire Staff

Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) bludgeoning damage plus 7 (2d6) fire damage.

Shadowfrost Bolt

Ranged Spell Attack: +8 to hit, range 150 ft., one target. Hit: 9 (2d8) necrotic damage plus 7 (2d6) cold damage.

Shadow Geyser (Recharge 6)

The shadow river lord expels a geyser of shadowy water from its staff in a 30-foot cone. Each creature in that area must make a DC 16 Dexterity saving throw, taking 21 (6d6) necrotic damage and 21 (6d6) cold damage on a failed save, or half as much damage on a successful one.