Also on another MoO race, the Darloks. As well as other staples of scifi, the shapeshifting scum that hope to take over the galaxy.
Unknown mechanism
-Darloks from Master of Orion. These mysterious aliens are despised by all for their insidious ability to mimic any shape or form. They're universally reviled and feared for their cunning spy capabilities.
Mechanism: Unknown.
Liquid morphing
-Changelings from DS9. Rulers of the Gamma Quadrant's Dominion, the Changelings rule from the shadows, content to let the day-to-day administration of their mighty empire be conducted by thralls like the Vorta, Jem'Hadar and Karemma. They have a hatred of 'solids' and dream of a future where their brand of 'order' reigns over the galaxy.
Mechanism: They appear to be liquid based, which allows them to shape their hands and limbs into weapons.
-T1000 from T2. The machines from the future, Skynet has decided that Humanity must be extinguished. Well, they lost. Boo hoo, wah wah.
Mechanism: Similar to the Changelings, but they're based on a metallic substance rather than an organic one.
Esoteric muscle control
-Zam Weesal from AOTC.
Mechanism: Hmm... this one appears to change faces rather than body mass. Leads one to think this would only be useful to fool humanoid races solely.
-Captain Garth of Izar, from TOS
Mechanism: Like Zam.
-Marta, from STVI: TUC.
-Facedancers, from dune.
Unique
-Chirpers, from Traveller. Small, winged lizards that seem commonly related to the Droyne (themselves a possible or theoretcal offshoot of the Ancients). Chirpers can make themselves invisible. Not to visual recording devices, but to people's perceptions. Thus, this technique lies in the realm of psionics. Invisibility might not be the same as changing one's shape but it's similar enough to be counted.
-Salt Vampire, also from TOS
Mechanism: This one is funny. Nancy Crater is seen being slapped around by Spock, with his Vulcanian strength, and she wasn't pummeled. The mass of the salt vampire might have something to do with that - it could be as strong as a bear for example - but the image of Nancy Crater, a middle-aged woman, was maintained.
But we ALSO know that different people see different things, McCoy saw a young Nancy, Kirk saw an older Nancy, and the Crewman saw a hot blonde sexpot begging to be fucked. This suggests to me that they were partially psionic, and thus that explains their mechanism for changing appearance.
-Chameleon armour, from Predator, Traveller. And of course the lizard in question.
Mechanism: This form of camoflage allows the wearer to mimic his immediate environment. They don't change shape as such, but change colour.
Any others?