Nimbus Terrafaux was rumored to be a black kickboxer in the first Mortal Kombat game. The rumor held that the series' creators wished to be politically correct by adding an African-American character. He could allegedly be unlocked when Reptile appears and says "look to la luna." When this was happened, the player could enter a code which would unlock Nimbus.
The Nimbus Terrafaux character was later revealed as a creation of Electronic Gaming Monthly as part of an April Fool's Day joke. They had previously interviewed Ed Boon about the subject of a new Mortal Kombat game, and he mentioned the secret kickboxer character, amongst several other "hidden" characters. The magazine then intentionally published false information on this character, complete with phony screenshots and a fabricated storyline of his tournament involvement. The factuality of this character was debated for a long time, and the search for "Nimbus Terrafaux" was a mission taken on by many Mortal Kombat fans.
The name Terrafaux lends a hint that this rumor was false. Terra being Latin and Portuguese for Earth, and faux being French for fake. Following the introduction of Jax, the series' first real African-American character, rumors concerning the character's existence faded.