|Undines or aquatic elves|
Most Undines (Pathfinder) and Water Genasi (D&D) largely resemble aquatic elves, so can be built in the same way.
For a Cecaelia (Pathfinder Bestiary 3 or True20 Freeport: The Lost Island), replace the fish tail with the tentacled bottom piece from a Squid Warrior (Atlantis) or Alien Commander (Alien Conquest). (The Disney Minifigures series, due out in May, will include Ursula, who will make an excellent cecaelia.) Or, if you don't mind the body being grossly oversized for a Medium figure, attach a minfigure torso to the studs on the top of an octopus's head.
|Sahuagin and four-armed mutant|
Other fish-like races, such as Locathah and Kuo-Toa, can also be built in the same way as sahuagin. Gungans and the Alien Conquest aliens also make good locathah or kuo-toa.
|Sea hag and merrow|
For a Sea Hag or Greenhag, use a witch (preferably a green-skinned one), or the head and torso of a Medusa (Minifigures Series 10). In my Freeport game, I built a sea hag using the Alien Avenger's head (Minifigures Series 9) and a robed statue torso (see photo).
That covers the major underwater humanoid races. Future columns will cover other types of aquatic creatures.