Satan

Satan is the opposite of god, a horned demon.

Appearances in LMMCU

 * Metaworld: Some of the characters say "What in the devil!" which means "What the Hell". Not only is hell Satan's mansion, but this is specifically mentioning the devil. In addition, one of the episodes goes over Jesus and Satan, and involves Satan, obviously. As in the New Testament, Satan attempts to turn Jesus unholy, but Jesus' multiple refusals allow him to pass the test. In this instance, rather than appearing looking like a burned corpse with horns, Satan appears as a pale man with a big nose and long black hair.
 * Galaxy Adventures: Despite the show attempting to avoid Religious references, not only are there references to God, Heaven, Hell, and Jesus' Cross, there are also references to Satan, such as Diablo Philip (Diablo is "devil" in Spanish"), Satanic Noises being heard from the "Solar Flare" theme, and various uses of "Speed Demon" (albeit indirectly Satanic), among others.