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)
A blue, wolf-like monster with horns on his head. He is a feared thief and bandit known as "Tiger of the Wind". He was the leader of a pack of rogue mixed-breed Tigers that were isolated from all humans. Eventually, he met up with Genki. At first, he looked down upon Genki's optimistic and caring nature. Tiger had a rough past that changed him forever, giving him a jaded and cold view of life. However, after listening to Genki, he has learned to care more for others. A clan of Dinos commanded by Moo killed off Tiger's pack, so he joined up with Genki's team in hopes of finding and defeating Moo. Tiger is extremely fast and powerful in battle. He uses an array of swift attacks, as well as firing electricity from his horns and using ice-based attacks. Tiger once had a younger brother named Gray Wolf. They lived together as orphaned pups. Eventually, they built a pack of mixed-breed Tigers. When Tiger first met Moo, the giant monster killed every last member of Tiger's pack, and kidnapped Gray Wolf, leaving Tiger to die. Tiger would later find out the cold, harsh truth of what happened to his brother. Tiger was the Phoenix's anger. (Source: Wikipedia)