Monev the Gale is the first Gung-Ho Gun to fight Vash. Knives locks him in a cell to train his body for twenty years in order to gain the skill and power required to kill Vash. He wears a powered battle suit and carries two high-powered chain guns on his arms. These guns fire extremely fast due to the pressure chambers located on his back, and have tremendous stopping power, enough to tear through entire buildings. He also carries a wide variety of weapons in a big cloth rucksack, including an enormous minigun, powerful enough to punch through a bank vault. (Owing to Hirahano's love of MacFarlane related products, as well as the characters name and appearance, he is more than likely a reference to Venom.) (Source: Wikipedia)
Midvalley the Hornfreak is a violent musician who is able to use his saxophone, Sylvia, to synchronize sound waves with pain, causing physical damage. He also is capable of neutralizing sounds by playing counter-frequencies. He and his band originally just kill for money until being found by Knives, who kills all except Midvalley. He dislikes both Legato and Knives, which leads him to try to kill Legato, though he is quickly killed himself. Legato uses Midvalley's body to attack Hoppered, and it is buried with his saxophone on his gravestone afterward. He has a smaller role in the anime, mainly acting as Legato's bodyguard until fighting Vash, and killing himself after overloading his saxophone. (Source: Wikipedia)
Leonof the Puppet-Master is an elderly man who controls a large number of puppets with an elaborate system of strings. He can manipulate them to look like real people, and uses them to do horrible things to people close to Vash. His real name is Emilio, having known Vash during his childhood. His love interest dies sometime after, and he goes into puppet making to mend his broken spirit. (Source: Wikipedia)
A flamboyant ninja demon working with Hoshiyomi to retrieve the Ken blade from Akitoki Hojo. His powers include summoning fire and transforming into a giant bird.
A duelist god said to not have lost a single duel, but in truth he is actually a pretty shoddy duelist and only won due to other people letting him win since he was the Pharaoh. (Source: Yu-Gi-Oh! Wikia)
NASA-built Super-AI robot, model number XCR-13 ("XCR" standing for "Experimental Cosmo Robo"). Mic Sounders the 13th is a relatively small red and blue robot of extremely blocky construction, with a monitor for eyes that changes to express a wide range of emotions (for example, on occasion it has turned into an image of GaoGaiGar's face when Mic is feeling brave). He has no actual abilities or powers to speak of, short of riding around in an almost cartoonish yellow flying vehicle called Baribarien. Mic first appeared having escaped his containment unit, at which point he made his way to a radi-robo (radio-controlled robot) competition that Mamoru Amami was participating in. During most of his first appearances, Mic was solely a comic relief character, often attempting to fly into a dangerous situation to assist GaoGaiGar only to be knocked far away with a cry of "Ohhh noooooooooooooo!" Eventually Mic gained the ability to transform into his true form; that of a tall blue and red robot seemingly designed after a rock-and-roll singer. While in this form, Baribarien transforms into a mobile stage (named Studio 7, a homage to the producers of the series), which it does by simply flipping over while Mic transforms. While in this mode, Baribarien produces most of Mic's musical equipment, which consists of a flying V keytar known as Dazzling VV, a pair of Thundering V microphones and a Sparkling V roofie harmonica. Mic's combat abilities are entirely based on sound manipulation - the programs to do so are stored in the form of various Discs stored in his Studio 7. In addition to the general-purpose Disc M and Disc P, Mic has the dangerous Disc X and later the much more powerful Disc F. Mic sports a distinct accent in both of his forms. In his Cosmo Robo form, he adds "Demone!" to the endings of most of his sentences, whereas in Boom Robo form he has a tendency to shout phrases equivalent to "It's awesome!"