This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Onza (Aztec and Latin American folklore)
The Spanish name onza derives from the Latin lynx, lyncis, and is equivalent to the English word "ounce", originally applied to the lynx but now more commonly to the snow leopard (Panthera uncia). There are old texts written by Spanish conquistadors about the onza, but they might refer to the jaguarundi, which is known as onza in many Mexican states.
The onza was described as being smaller then a cougar, with a remarkably slender body build. It had long, skinny legs, an exceptionally long tail for its body size, and enlongated ears somewhat like a wolf's ears. It tended to have faint striping, especially on the lower legs.