Archnaiad

Naiads live in and near water. They might be spotted among rivers and lakes, on isolated shores, or amid coral labyrinths and deep sea fumaroles. Wherever rivers and seas show their variety and force, naiads gather to revel in nature’s might. Individual naiads often grow fixated with a single type or body of water, potentially preferring a deep sea trench, coastline, or river system above all others. Over time, such a resident nymph often becomes connected with their aquatic home through sightings and stories, becoming a guardian of the place and, in effect, a manifestation of its personality.

Aquatic Collectors. Curious by nature, naiads often seek out what the seas and rivers claim. As a result, they might be found among sunken ruins and shipwrecks, sifting through the remains for whatever catches their eye. Living creatures aren’t exempt from this curiosity, either. Naiads are known to befriend aquatic creatures, or even to keep modest menageries. The occasional star-crossed castaway has even been known to become part of such collections.

Nymphs

Divine servants that inhabit unspoiled corners of the world, nymphs protect places of natural power and infuse their surroundings with the magic of Nyx. Some are benevolent and aid those who live off the land, while others embody violent aspects of nature. In either case, nymphs generally avoid other sapient creatures, preferring to mind the cycles of nature, the daily interplay of wild animals, or other cosmic forces. Occasionally, though, groups of the same kind of nymphs congregate in a place of natural power or beauty. In times of special need, deities tied to facets of nature might employ nymphs as messengers, guardians, or scouts.

Immortal Nature. A nymph doesn’t require food, drink, or sleep.

Archnymphs

 Some nymphs can become so suffused with wild magic, be raised by an archfey or Wild Spirit, or otherwise empowered beyond their normal means. These Nymphs become Archfey themselves, and claim a singular body of water as their domain. 

To and Fro. A secret closely guarded by nymphs are the use of Archnaiad's lairs as portals into the Feywild. As the Feywild mirrors the Prime Material, an Archnaiad's domain allows it to traverse between the planes as desired. Consequently, any other creature can use the pool of water as a portal to the Feywild as well. 

An Archnaiad's Lair

An archnaiad chooses a body of water it has attended to and guarded for her entire life such as a river or a lake. Upon becoming an Archnaiad, the body of water becomes her lair, and consequently a portal to the Feywild. Such lairs may be home to other naiads or similar aquatic fey. These beings do not regard the lair as their home and possess great respect for the Archnaiad.

An Archnaiad encountered in her lair has a challenege rating of 17 (18,000 XP)

Lair Actions

On initiative count 20 (losing initiative ties), the archnaiad can take a lair action to cause one of the following magical effects, but can’t use the same effect two rounds in a row:

• Caverns, tunnels, and pools of water within 120 feet of the archnaiad become clear and attract nearby wildlife. 
• The archnaiad conjures a 15-foot cube of water that fills an unoccupied space she can see within 30 feet of herself, then moves the water in a straight line up to 60 feet, after which the water disperses. Any creature that comes into contact with the rushing wave must succeed on a DC 18 Strength saving throw or be knocked prone by it and pushed 15 feet along its course.
• The archanaid can force all creatures within 60 feet of herself that are in within any body of water (even a puddle) to make a Strength saving throw (save DC 18). On a failed save, each creature is restrained as they are slowly weighed down 20 and begin drowning. If a creature is underwater when this action is used, they must make a Constitution saving throw instead, losing 1d3 minutes of air in the process. A creature can repeat the Strength save at the end of each of its turns, ending the effect on a success. 

Regional Effects

The region surrounding an Archnaiad's lair is warped by the creature’s fey presence, creating any of the following effects:

• There’s a noticeable increase in the populations of fish, crustaceans, and other aquatic life befitting a salt or fresh water area
• The water of an archnaiad's lair can sustain a creature for up to 24 hours with a single drink. Such water is clear, refreshing, and pure.
• The archnaiad can alter the appearance of her domain as she sees fit. She can make the water appear murky, tainted, or a different color altogether. She can also create illusions of creatures and objects as she wishes. These illusions act as if she had cast the silent image spell, and there can be as many or as little as the archnaiad desires
• Plantlife for up to 500 feet around the body of water appear lush and healthy, blessed by the magic of the Archnaiad. Such greenery acts as magical difficult terrain for anyone with foul intentions towards the Archnaiad, the lair, or both.

If the Archnaiad is killed, these effects end after 2d6 days.