Merfolk

Doesn't Breath (Gills)

You can extract oxygen from water, allowing you to remain submerged indefinitely. You suffocate if the water contains no dissolved oxygen. You are immune to strangulation and “the bends.”

Enhanced Move 1 (Water)

Merfolk have Enhanced Move when in the water.  Enhanced Move doesn't change your Base Speed, however it gives you the option of increasing how fast you're moving up to double your base move.  To move at speeds in excess of your base Speed you must move at your base Speed for one round before accelerating past that.  When moving at speeds above your base speed movement has more rules for handling, changing direction, and slowing down.  

Go here for a more in-depth look at how High Speed Movement works.

Nictitating Membrane 3

You have a transparent lens over your eyes that you can open and close like an eyelid. This lets you see normally underwater, and protects your eyes from sand, irritants, etc. Your Nictitating Membrane provides your eyes (only) with DR 3 and adds +3 to all HT rolls concerned with eye damage.

Pressure Support 1

Every character has a “native pressure.” For ordinary humans, this is the pressure of Earth’s atmosphere (“1 atmosphere”). As a Merfolk you can survive at pressures between your native pressure and 10 times that, allowing you to live and explore the water along the continental shelves.  However the pressure on the bottom of the ocean floor and especially the depths of the deepest canyons can far exceed this tolerance.

Slippery 1

You are hard to hold! The scales on your lower body are smooth and coated with a thin layer of mucus that helps you glide through the water and protects you. This gives you +1 on all ST, DX, and Escape rolls to slip restraints, break free in close combat, or squeeze through narrow openings.

Speak Underwater (Aquatic)

You can talk normally while submerged, and you can understand what others say while underwater.  This doesn't work well crossing between mediums, you still can't talk from under water and be understood by those outside the water and vice versa.

Temperature Tolerance 2 (Cold)

Every character has a temperature “comfort zone” within which he suffers no ill effects (such as FP or HP loss) due to heat or cold. For ordinary humans, this zone is 55° wide and falls between 35° and 90°. For Merfolk adapted to living in the cool water of the ocean this zone is expanded, lowing the cold end of the spectrum by HT*2.  Temperature Tolerance confers no special resistance to attacks by fire or ice unless the only damage is a result of a rise or fall in the ambient temperature. In particular, it cannot help you if your body temperature is being manipulated. 

No Legs (Aquatic)

You can't really move on land, but you are adapted to movement on or in water, like a fish. Calculate Basic Move and use this as your basic water Move. Your ground Move is 0, though you may crawl. You suffer no skill penalties for working in or under water. However your mobility depends on fins that you can’t armor.

Dependency (Water, Daily)

You must regularly spend time in water in order to survive. If you fail to do so, you start to lose HP and will eventually die. Lose 1 HP per hour after missing a daily dose. You need spend at least one hour per day in order to avoid damage. 

Alcohol Intolerance

Merfolk are used to being saturated with water, it passes through them more quickly than the land folk, as a result Alcohol “goes right to your head.” You become intoxicated much more quickly than normal. You get -2 on any HT roll related to drinking.

Subraces

Cecaelia 

Octopus Merfolk

Cost: 15 points
Changes: HT -1 [-10], Nictating Membrane 1 [-2]
Additions: Amphibious [+10], Extra Arms (Extra-Flexible, Foot-Manipulators, No Attack, Weak) [+27], No Legs (Semi-Aquatic) [0]
Deductions: Enhanced Move (Water) [-20], No Legs (Aquatic) [+10]

Amphibious & No Legs (Semi-Aquatic)

You can't move well on land, but you are adapted to movement on or in water, like an octopus. Calculate Basic Move and use this as your basic water Move, however your Basic Move while on land is equal to 1/5 your Base Move. You suffer no skill penalties for working in or under water. However your mobility depends on tentacles that need to remain mobile and unencumbered with armor.

Extra Arms (Extra-Flexible, Foot-Manipulators, No Attack)

In place of a fishy lower half you instead have the body of an octopus, with just 6 highly flexible tentacle arms that allow you to move and manipulate objects.  When manipulating objects with your tentacles it is more difficult to move, reducing your Base Speed by 1 yard per tentacle occupied in this way.  Your tentacles are strong but lack fine dexterity and make for poor limbs to attack with.  You may not attack or kick with them, however if you get into a grapple you gain +6 to your Grapple or Judo skill roll because of the extra limbs.

Korathos 

Korathos are the Crab-Folk of the ocean floors.

This one's pretty complicated so I'm going to include the altered stat line instead of a list of changes as I have with other subraces. 
The Korathos subrace costs an additional 20 points for a total of 80 points.

ST +4 [+40], HT [+10]
HP +1 [+2], Per -1 [-5], Speed -0.25 [-5]
Amphibious [+10], Claws (Blunt Claws) [+3], Constriction Attack [+15], Damage Resistance (Can't Wear Armor) 3 [+9], Doesn't Breath (Gills) [+10],High Pain Threshold [+10], Injury Tolerance (No Vitals) [+5], Lifting ST +2 [+6], Pressure Support 2 [+10], Reduced Consumption 1/3 (Cast-Iron Stomach) [+2], Temperature Tolerance 3 (Cold) [+6], Speak Underwater (Aquatic) [+5]
Dependency (Water, Daily) [-15], Ham-Fisted (-3) [-5], No Wrists (-3) [-5], Numb [-20], Can't Float [-1]
Skills: Swimming +1 rank [+1]

Amphibious

You suffer no skill penalties for working in or under water, and you use your full base move for movement through water.

Claws (Blunt Claws), Ham-Fisted, No Wrists, Numb, and Constriction Attack

In place of hands Korathos have crab like claws.  

These claws lack fingers, thumbs, and wrists making them very bad at manipulating objects, especially managing fine detail work.  

This combination of Advantages and Disadvantages means that Korathos have a total of -9 to fine detail work involving skills like art, engineering, and fast draw. They also have a -6 to less detailed work that involves the use of hands, such as wielding weapons, with the lack of proper grip and no wrists they can't leverage any kind of weapon effectively.  

However, these penalties don't apply to unarmed attacks. Korathos have strong claws that deal Crushing damage at Thrust +1 per die, and deal Constriction damage to anything they can grip in their claws. To deal constriction damage you must first successfully grapple your intended victim, whose Size Modifier cannot exceed your own. On your next turn, and each successive turn, roll a Quick Contest: your ST vs. your victim’s ST or HT, whichever is higher. If you win, your victim takes damage equal to your margin of victory; otherwise, they take no damage.

Note: The Lifting ST +2 bonus to strength applies to the Quick Contest for Constriction Damage.

Damage Resistance 3 (Can't Wear Armor)

When you are hit, reduce any damage you suffer by 3 before the damage is applied to your hit points.  However, Korathos have unique body shapes, and their exoskeleton is very rigid making standard armor impossible for them to wear.

Doesn't Breath (Gills)

You can extract oxygen from water, allowing you to remain submerged indefinitely. You suffocate if the water contains no dissolved oxygen. You are immune to strangulation and “the bends.”

High Pain Threshold

Korathos have few pain receptors, so, while they are just as susceptible to injury as other creatures, they just don't feel it as much.  Korathos never suffer shock penalty when injured.  Additionally they gain +3 on HT rolls to avoid knockdown and stunning, and gain +3 to resist physical torture.

Injury Tolerance (No Vitals)

Korathos physiology is very different than mammalian humanoids, they have a hard exoskeleton, while there insides are comprised of muscle and organs that are somewhat harder to get at.  Treat all strikes to the 'vital organs' or 'groin' as torso strikes for the purpose of determining damage.

Lifting ST +2

You have lifting capacity out of proportion to your mass. Add your Lifting ST to your ordinary ST when you determine Basic Lift for the purposes of carrying, lifting, pushing, and pulling. Lifting ST also adds to ST in situations where you can apply slow, steady pressure (grappling, choking, etc.). 

Lifting ST does not boost ST (or Basic Lift) for the purpose of determining HP, throwing distance, or damage inflicted by melee attacks or thrown weapons.

Pressure Support 2

Every character has a “native pressure.” For ordinary humans, this is the pressure of Earth’s atmosphere (“1 atmosphere”). You can withstand pressures between your native pressure and 100 times that. This enables Korathos to survive anywhere in the oceans, save the deepest trenches.

Reduced Consumption 2 (Cast-Iron Stomach)

Korathos are bottom feeders, walking the sea floor and eating whatever they can get their pincers on. You require the standard amount of food and water, but the quality is irrelevant. You can eat rotten vegetables and fuzzy blue-green meat, and drink dishwater and sour milk. Instead of reducing how often you must eat, reduce your demands on life support (and your food costs) by a like amount: to 1/3 normal.   You get a +2 bonus to resist the effects of food-borne poisons or diseases not tailored expressly for you. 

This doesn't change how those things taste, and while you are fully capable of stomaching the food you may desire foods with an improved taste if they are available.  

When you claim the reduced cost benefit for this advantage anyone watching you eat gets a -3 on reactions!

Speak Underwater (Aquatic)

You can talk normally while submerged, and you can understand what others say while underwater.  This doesn't work well crossing between mediums, you still can't talk from under water and be understood by those outside the water and vice versa.

Temperature Tolerance 3 (Cold)

Every character has a temperature “comfort zone” within which he suffers no ill effects (such as FP or HP loss) due to heat or cold. For ordinary humans, this zone is 55° wide and falls between 35° and 90°. For Merfolk adapted to living in the cool water of the ocean this zone is expanded, lowing the cold end of the spectrum by HT*3.  Temperature Tolerance confers no special resistance to attacks by fire or ice unless the only damage is a result of a rise or fall in the ambient temperature. In particular, it cannot help you if your body temperature is being manipulated. 

Can't Float

Korathos are crustaceans designed for bottom feeding and walking the floor of the ocean, less for swimming.  While they're capable swimmers they don't float, they sink.