Moo is a breed of Dragon that has a ??? sub-type, first introduced in Monster Rancher 2. It is only obtainable by using the CD Beck: Mellow Gold, and is immensely powerful. It has the same color scheme as Ripper, leading to the belief that it has a Ripper sub-type. Moo is the main boss in the Monster Farm Lagoon game, and uses its dark powers to take over several other monsters (a Kikimo and a Tiger) and make them Moo-hybrid level bosses as well. Moo also has several modes, one being his "Larva Mode" in Lagoon. He has less power and is mostly just a black spirit form of himself. Later, the inhabitants of the Warp Dimension create their own version of Moo by using his DNA, and his "Warp Mode" becomes the main level boss of Monster Rancher EVO.
Moo is the main antagonist of the anime series, and spends most of it in a merged human/monster form. He spends a long time attempting to reclaim his huge Dragon body.
Monster Rancher 2: This dreadful looking dragon hardly appears even in legends.
Mu is a Japanese word meaning "void."