Rai-Dei is a samurai who seeks the knowledge learned only when facing death. He carries a sword with a built in gun that can be fired from the hilt, and is able to swing it with enough force to create a sonic blast. In the anime, he expresses anger in the fact that Vash is refusing to make his mark true and aim to kill, claiming he wants "a real battle." In the manga, he wears "roller skates" that allow him to move at phenomenal speeds. (Source: Wikipedia)
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 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)
The Great Toad Sage is the oldest and most respected toad of all the inhabitants of Mount My�boku. Because of his age, the other toads affectionately call him Great Honorable Geezer. He is famed for his highly accurate prophecies. Being several thousand years old, he is the oldest and most respected among the population of Mount My�boku. At his great age, the Great Toad Sage seems to constantly smile and tends to have his eyes closed or squinting. He is portrayed and described as being senile, and sometimes out of touch with his present situation, so he does tend to forget things easily and quite quickly. However, when reminded, he is still able to remember things and can easily tell things very precisely. As a sage, he is also very wise, and is quick to stop Shima and Fukasaku from bickering and encourages harmony. It would seem that unlike most other toads, he actually has respect for Jiraiya, and has urged both Shima and Fukasaku to cooperate with him