Amphibious. The merrow can breathe air and water.
Spellcasting. The merrow is a 6th-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 13, +5 to hit with spell attacks). The merrow has the following druid spells prepared:
Cantrips (at will): druidcraft, minor illusion, shocking grasp
1st level (4 slots): cure wounds, fog cloud, thunderwave
2nd level (3 slots): hold person, mirror image, misty step
3rd level (3 slots): dispel magic, lightning bolt (see "Actions" below), sleet storm
Harpoon. Melee or Ranged Weapon Attack: +6 to hit, reach 5 ft. or range 20/60 ft., one target. Hit:11 (2d6 + 4) piercing damage. If the target is a Medium or smaller creature, the merrow can pull it 10 feet closer.
Lightning Bolt (3rd-Level Spell; Requires a Spell Slot). The merrow unleashes a stroke of lightning in a line 100 feet long and 5 feet wide. Each creature in the line must make a DC 13 Dexterity saving throw, taking 28 (8d6) lightning damage on a failed save, or half as much damage on a successful one.
Some of the many merrow that dwell in the watery shadows of the Menagerie Coast learn to harness the magical aspects of the elements. Often working as guides leading merrow hunting parties, some of these shallowpriests rise to become powerful leaders, inspiring their clans to terrorize coastal communities and passing ships.