Homebrew, Mythic Odysseys of Theros (5e)
Innate Spellcasting. The naiad's spellcasting ability is Charisma (spell save DC 14). It can innately cast the following spells, requiring no material components:
Amphibious. The naiad can breathe air & water.
Invisible in Water. The naiad is invisible while fully immersed in water.
Magic Resistance. The naiad has advantage on saving throws against spells & other magical effects.
Multiattack. The naiad makes two slam attacks.
Slam. Melee Weapon Attack. +5 to hit, reach 5', one target. Hit: 8 (1d10 + 3) bludgeoning damage.
Watery Embrace. Once per turn, if the naiad successfully hits a creature with a melee weapon attack, it can also attempt to grapple the target. If the naiad is immersed in water, it has advantage on its grapple check & advantage against any attempts by the creature to escape the naiad's grapple.
Any Climate; Coastal, Seas, Swamps; Feywild, Elemental Plane of Water