The Rigellian hypnoid was a pink, six-legged reptile native to the Rigel system. They had the ability to create illusions in the mind of nearby observers.
Harry Mudd used a Rigellian hypnoid to trick miners on the planet Motherlode into believing that his love potion crystals would make a woman fall in love with him, causing the shapeshifting creature to assume the appearance of Lora. The swindle was exposed by Spock, however, and the Rigellian hypnoid was unmasked. (TAS: "Mudd's Passion")
The pink coloration and six-legged nature of the hypnoid was not scripted; in the final draft script of "Mudd's Passion", the hypnoid is described simply as "a small, reptilian creature".