Merfolk

Merfolk are mythological creatures that have the upper bodies of humans and the lower bodies of a marine animal, almost always a fish. They originated in medieval folklore as mermaids, creatures that would seduce blueballed sailors to drown them (mermen were invented sort of as an afterthought to explain procreation). They are prominently featured in MTG, RPGs, and even 40k had a minor aquatic race at one point. Creatures similar to merfolk can also be found in many videogames, such as the Zora from The Legend of Zelda, the Naga from Warcraft, and the Slithereen from Dota2.

Dungeons & Dragons and Pathfinder generally have given merfolk only lackluster attention, as their unique body configuration makes them to all practical purposes useless on your typical land-based campaign, but, if you add them into a "surfacers gone underwater" campaign (itself a rarity), they tend to be overpowered, as they are faster and don't need to worry about breathing underwater. D&D usually tries to push the Triton over the merfolk as a consequence, as Tritons at least can try to partake in both underwater and traditional campaigns.

Still, despite their issues, /tg/ has had a spattering of threads dedicated to merfolk over the years where it has discussed how an underwater civilization would develop, and many people have wished to use merfolk characters or merfolk cities in their campaign. Unfortunately, most settings have rules that are not conducive to using merfolk as player characters, fluff that does not include merfolk as a major power, and a lack of effort to describe a thriving merfolk civilization.

D&D Third Edition Merfolk and similar races

D&D Third Edition is notorious for a lot of things, one of which is its absurdly large number of playable races, and its even larger number of NPC monsters that can be adapted for use as PC races. It's therefore no surprise that 3e would have a shit ton of underwater and/or amphibious humanoid races comparable to merfolk. For example:

• Aquatic Elves from the 3.0e Monster Manual I; they were reprinted with new weapon proficiencies in Stormwrack
• Selkies, a quasi-playable NPC race of beautiful women whose favorite hobbies are shapeshifting into seals and having sex with human men, hopefully not in that order, from the 3.0e Fiend Folio
• Tritons, which appeared as a monster class in Savage Species and a quasi-playable NPC race in the 3.5e Monster Manual I
• Actual Fucking Merfolk as a quasi-playable NPC race in the 3.5e Monster Manual I
• The Dargonesti and Dimernesti, two races of Sea Elves from the Dragonlance campaign setting
• Sea Kin, a "humans with gills" race from Races of Destiny
• The Aventi from Stormwrack, which are basically the same fucking thing as Sea Kin
• Shoal Halflings, also from Stormwrack
• Nereids, a quasi-playable NPC fey/elemental/extraplanar version of merfolk, also from (le sigh) Stormwrack
• All manner of water elementals, water half-elementals, water mephits, water mephlings, water genasi, etc... not all of them live underwater and not all of them are playable but we're not going to sort through them at the moment.

Additionally, any humanoid race can be turned into a pseudo-merfolk variation with the addition of the Aquatic template, from... you guessed it... Stormwrack.

Note that this list specifically excludes races that are merely good at swimming but must still breathe air and live on land, which, of course, Third Edition also has a fuckton of (like the Darfellans... guess what book they're from).

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Pathfinder Merfolk

With a +2 in dexterity, constitution, and charisma with no stat minus, +2 natural armor, and unlike some amphibious races not drying up if they're on land, Merfolk are a fantastic race. The only problem? Sloooow on land. 5 feet move (15 with a trait- still half of everyone else). If you pick a class that gets a way to give them respectable movement and/or you just don't mind being the slowest one around, a solid choice.

They have a Drow equivalent Deep Merfolk race, grey-skinned merfolk who live in the lightless depths of the seafloor.

Monstergirls

Mermaids are naturally among the most common monstergirls. They have a very similar problem to centaurs though, in that if they're a nonhuman animal from the waist down, where's their vagina? Also like with the centaur, different approaches to "The Mermaid Problem" have been taken. Some give merfolk the genitalia of fish, thus having fertilization occur externally (sexual interactions with humans are typically of the oral variety in this case). Others instead have the fish part start just below the genitals, which would logically result in a weird hole through the middle of their bodies. Still others have the fish part start above where human genitals would be and just slap on a forward-facing human vagina at waist-height. The simplest approach taken is making mermaids limited shapeshifters, capable of transforming their tail into legs. This is typically paired with a duration limit or need to return to water within a limited time to stop them from being reduced to strictly better humans and keep them sea creatures.

On their page titled "The Mermaid Problem," TVTropes of all sites puts forth the clever idea of replacing the fish tail with a dolphin tail. This is brilliant for more reasons than that article seems to realize, since not only does it simplify a lot of the internal biology by making them fully-fledged mammals, but there's also the fact that dolphins are actually notoriously perverted in regards to sexual behavior, with individuals of both sexes often trying to bone dolphins and non-dolphins alike, and there being so much sex overall that the females of some species have evolved an additional pelvic orifice that exists for the sole purpose of sex. On top of that, since it's hard to hold onto someone you're constantly thrusting into when you A) are floating around in the ocean, B) don't have arms, and C) can't coil around them like a snake or eel, dolphins of both sexes actually have MOTHERFUCKING PREHENSILE GENITALS. Yeah, you're probably getting several ideas right now, aren't you, you perv?

MGE

It'd be more surprising if the Monster Girl Encyclopedia didn't have a mermaid mamono. They are portrayed as incurable romantics who yearn to find that special someone. They also have quite a family tree, with Merrow (their perverted cousins), Sea Bishops (mermaid clerics of the sea goddess), Mersharks (aggressive shark-based mermaids), Unagi Joro (lamia-esque eel-maids from Zipangu) and even Selkies (wereseals) making up part of the Mermaid class of mamono.

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See Also

• Merfolk/Homebrew for an extensive piece of homebrew all about merfolk.
• Cerulean Seas Campaign Setting (Pathfinder compatible)

The Races of Pathfinder
Player's Handbook:	Dwarf - Elf - Gnome - Half-Elf - Half-Orc - Halfling - Human
Advanced Race Guide:	Aasimar - Catfolk - Changeling - Dhampir - Duergar Drow - Fetchling - Gillman - Goblin - Grippli - Hobgoblin Ifrit - Kitsune - Kobold - Merfolk - Nagaji - Orc - Oread Ratfolk - Samsaran - Strix - Suli - Svirfneblin - Sylph Tengu - Tiefling - Undine - Vanara - Vishkanya - Wayang
Bestiaries:	Android - Astomoi - Caligni - Deep One Hybrid - Gathlain Gnoll - Kasatha - Munavri - Naiad - Orang-Pendak Reptoid - Rougarou - Shabti - Trox - Yaddithian
Adventure Paths:	Being of Ib - Kuru
Inner Sea Races:	Ghoran - Monkey Goblin - Lashunta - Skinwalker Syrinx - Triaxian - Wyrwood - Wyvaran
Ultimate Wilderness:	Vine Leshy
Blood of the Sea:	Adaro - Cecaelia - Grindylow - Locathah - Sahuagin - Triton
Planar Adventures:	Aphorite - Duskwalker - Ganzi