Physical Description: Merfolk have the upper torsos of well-built and attractive humans and lower halves consisting of the tail and fins of a great fish. Their hair and scales span a wide range of hues, with merfolk in a given region closely resembling each other. Merfolk can breathe air freely but move on dry land only with difficulty, and rarely spend long periods out of water.
Society: Merfolk live in massive, sprawling cities built on the ocean floor. Primarily built from stone, or occasionally grown from magically influenced coral, their structures rarely have a consistent ceiling and floor, instead being designed to swim or float through, with furniture and storage attached to any convenient surface.
There are five major kingdoms of Merfolk, confined to the five smaller oceans before the Cataclysm, they now spread across the ocean floor, struggling to hold together their sprawling empires. Four of the five are monarchies, led by a hereditary King or Queen who carries great magical power in their blood line. In the fifth kingdom the royal line was lost in the Cataclysm, and they are attempting a great experiment in democracy with the aid of advisers from the surface Republic of Theramacya.
Religion: The Merfolk gods consist of five ascended heroes of ancient myth. Each one is said to have founded one of the five kingdoms and is the ancestor of the ruler and patron of that kingdom. All are worshiped as a divine pantheon, but in each kingdom their ancestor is considered the king of the gods. As the empires expand, there is growing reverence for Atlaua, especially in the more rural undersea villages and deep wildernesses where the ancestor church seems so far away.
Relations: As a race, Merfolk are insular and distrustful of strangers, but individuals, especially adventuring Merfolk, break the mold and can be quite garrulous. With the rapidly expanding borders of their empires they have had to learn to be more diplomatic and willing to deal with outsiders in general, though each kingdom has its own idiosyncrasies with strangers.
Alignment: Merfolk concern themselves more with nature and the arts than with morality and ethical debates, and have a strong inclination toward neutral alignments.
Adventurers: Especially with the rapid growth of the kingdoms and constant skirmishes with other kingdoms and other undersea civilizations, there has been a population boom and also more and more disenfranchised former soldiers. Some of these individuals turn to mercenary work, but many turn to adventuring, ranging even wider to see more of the world.
Merfolk Racial Traits
+2 Dexterity, +2 Constitution, +2 Charisma: Merfolk are graceful, hale, and beautiful.
Medium: Merfolk are Medium creatures and have no bonuses or penalties due to their size.
Slow Speed: Merfolk have a base speed of 5 feet. They have a swim speed of 50 feet.
Aquatic: Merfolk are humanoids with the aquatic subtype.
Amphibious: Merfolk are amphibious, but prefer not to spend long periods out of the water.
Low-Light Vision: Merfolk have low-light vision.
Armor: Merfolk have a +2 natural armor bonus.
Legless: Merfolk have no legs, and cannot be tripped.
Languages: Merfolk begin play speaking Common and Aquan. Merfolk with high Intelligence scores can choose from the following: Aboleth, Dolphin, Draconic, Elven, Sylvan and Whale.
Alternate Racial Traits
The following racial traits may be selected instead of existing merfolk racial traits.
Darkvision: Some merfolk favor the lightless depths over shallower waters. Merfolk with this racial trait gain darkvision with a range of 60 feet and light sensitivity. This racial trait replaces low-light vision.
Seasinger: The beautiful voices of the merfolk are legendary. A seasinger gains a +2 racial bonus on Perform (sing) checks and a +1 racial bonus to the save DC of language-dependent spells. This racial trait replaces low-light vision.
Strongtail: A few merfolk have broad, strong tails that are more suited for land travel than the typical merfolk tail. Merfolk with this racial trait have a land speed of 15 feet and a swim speed of 30 feet.
http://paizo.com/pathfinderRPG/prd/advancedRaceGuide/uncommonRaces/merfolk.html with original content added