Yadokargo is the boss of the opening stage in Mega Man 8, a crab-like robot that protects Dr. Wily's secret base, and accumulated moss on its shell due to the long time it stood still. He pinches at Mega Man, leaps, and shoots bombs. His weak point is his brain, which is protected by his shell. When hit by a charge shot or one Mega Ball, his brain is exposed. When visiting the stage again, he can be easily be taken out with Flash Bomb or Tornado Hold, and can be destroyed instantly with Astro Crush (regardless of protection from his shell).

Tengu Man is a Robot Master from Mega Man 8. He is equipped with a razor-winged jet engine on his back that grants him high-speed flight, a retractable triple-bladed weapon on his arm, and the ability to summon cutting blades of air and whirlwinds to trap and blow his opponents to their doom. He fights with the boldness of a teenager, and speaks like one too, having noticeably brash and overconfident mannerisms. Tengu Man was created by Doctor Albert W. Wily, modeled after the Tengu, a Japanese yōkai, and was stationed within a high mountain range in Japan to occupy Mega Man.

In Mega Man & Bass, it is revealed that he survived the events of Mega Man 8, enlisting as a high-ranking member of King's Army to exact revenge on Mega Man for disgracing him in their previous battle. His stage is one of the two stages unlocked by defeating Ground Man, and is one of the few robot masters to grant two different weapons on separate occasions.

Clown Man is a mischievous clown-like Robot Master from Mega Man 8. He was originally an amusement park robot, but was stolen and remodeled for combat by Dr. Albert W. Wily to wreak havoc in somewhere in New South Wales, Australia. His leftover parts were used by Wily to create Frost Man.

Grenade Man is a Robot Master created by Dr. Wily visually designed after a hand grenade (specifically a Mk 2 grenade, aka a "Pineapple Bomb"), having a similarly textured stomach area, and a headpiece reminiscent of a striker lever. He is sadomasochistic, enjoying both inflicting and receiving pain, particularly through getting himself caught in the explosions he creates. He fights primarily using his Flash Bombs and other such high-explosive weaponry. A special Overdrive system is installed in him, allowing him to move very quickly and to temporarily boost his power.

During the events of Mega Man 8, he was stationed at a ammunition factory somewhere in Chile, causing havoc with his soldiers and explosive weaponry.

Frost Man is a combat Robot Master created by Doctor Albert Wily using the several leftover parts he used to create Clown Man. As result, he has poor oil circulation. Frost Man is large and physically strong, which he is proud of, but isn't very smart. In Mega Man 8, he creates havoc in Alaska. When Mega Man enters his room, there are several ice statues of Mega Man inside, and Frost Man crushes them all. Frost Man's ultimate goal is to turn Mega Man into a Kakigōri (or, in the English version, a popsicle) and eat him.

Sword Man is a combat Robot Master that was built by Dr. Wily to use an ancient sword that he stole from a museum. Unfortunately, Sword Man's sword was way too heavy, so the upper part of the body was fitted with an anti-gravitational device, and as such, both the upper and lower halves of his body can act independently of each other to improve his balance.

His main attack is Flame Sword, an attack that envelops his sword with flames for extra damage. Sword Man can also attack by spinning his upper part rapidly to cut enemies, and drops heavy statues. His stage from Mega Man 8 is a Cambodian Temple-like area shown located somewhere in Central Asia, but would be more southeast on the Asian mainland.

Search Man is a Robot Master created by Dr. Wily, designed to look like a soldier. During Search Man's construction, Wily had the idea that if he had two minds, he could be slightly wiser and stronger than other Robot Masters, and went off the idea of a two-man sniper in one. Unfortunately, Wily forgot to install two personalities, and because Search Man constantly switches himself from head to head, he gets himself confused. He can hide in bushes, hiding nothing behind one, a decoy behind two, and himself behind the last one. Search Man is one of the four Robot Masters that protected the barrier to "Wily Tower" and was placed somewhere in the forest of Congo, Africa.

Astro Man was originally built to work on a planetarium, but Dr. Wily modified him for combat, and he uses his abilities to confuse his opponents. Despite his great powers, Astro Man is modest and shy. He's easily startled, and thus not very reliable in battle; and more of a coward. He is the world champion at hide-and-seek.

In Mega Man 8, he is one of the four Robot Masters built to protect the barrier to the "Wily Tower", and was placed in a virtual-like area in the northwest of Europe, possibly Norway. Later, Astro Man was revived by King to occupy a similar area in Mega Man & Bass. He is one of the first three selectable Robot Masters in Mega Man & Bass, alongside Cold Man and Ground Man. Defeating Astro Man opens the stages of Dynamo Man, Pirate Man, and Tengu Man.

Aqua Man is a water-themed Robot Master that originally operated in a waterworks bureau managing water quality before being modified by Doctor Wily as a combat robot.

Designed with the ability to store water inside of himself and release it using a cannon on his arm, Aqua Man has the unique ability to control water. In order to attack, he can fire controllable jets of highly pressured water, or use his Special Weapon, the Water Balloon, to launch heavy spheres of water at his opponents. However, his internal water tanks are vulnerable to breakage from heavy impacts, especially from the Astro Crush's meteors.

Aqua Man seems to be some what flamboyant; evidenced by some of his taunts to Mega Man when encountering him, as well as using a rainbow to spell out his name. He is a mischievous and somewhat immature Robot Master, with a love for dirty jokes and puns and being something of an attention-seeker. He does not react well to serious situations however, and tends to be made fun of for his rather bulky design. In the Japanese version he adds "poyon" in the end of most of his sentence.

Duo is a character from the original Mega Man series. He is an extraterrestrial space police robot with the mission to eliminate the Evil Energy. His left hand glows to absorb and destroy the Evil Energy.

Duo chronologically first appeared in the beginning of Mega Man 8 fighting in space against an unknown Evil Robot with Evil Energy. As they collide into each other, they fall towards Earth and the two crash on an island. Mega Man is sent by Dr. Light to investigate the island, where he finds, and takes the broken Duo to Dr. Light while Dr. Wily gets away with the Evil Energy. After Dr. Light starts to repair Duo, and after the defeat of the first four Robot Masters, Duo awakes and goes after the Evil Energy in Dr. Wily's hideout. There he finds, and fights against Mega Man thinking he wanted to interfere with his mission, before realizing that Mega Man had a strong sense of justice. He then joins forces with Mega Man, helping him against Dr. Wily, and later saving his life.

Atetemino is the first boss of the Wily Tower in Mega Man 8, which likes to do mischief. It is kind of like the Mega Man version of "Whack-A-Mole" as the player must hit the bagworm (the one that taunts before the battle begins).

Bliking is the boss of the second Wily Tower stage. It is a powerful combat robot created by Dr. Wily. Because of an emergency, it was not painted. Bliking can only be damaged when its wings are fully extended. It attacks by releasing mines from the top, using six lasers from the wings, shoot missiles from its tail, and tries to ram at the player. It is vulnerable to Astro Crush.

The Green Devil is a improved version of the Yellow Devil that appears in Mega Man 8 and Mega Man & Bass. His body is made of a thick slime-like substance that can be manipulated by the eye in the center.

In Mega Man 8, Green Devil is the boss of the third Wily Tower stage and attacks like the other Devils, except that he can turn his goo into spikes or rush forward as a wave of goo. A feature unique to this Devil is that his eye is covered by a bubble-like coating, preventing shots from hitting it in humanoid form. The goo must be peeled back by striking the chest with attacks (the Flash Bomb instantly does this, as does the Arrow Shot and Laser Shot.), then striking the eye, preferably with Thunder Claw.

In Mega Man & Bass, the Green Devil is the first boss and covers King's escape from the Robot Museum. He is weaker than the Mega Man 8 version, and takes increased damage from the Mega Buster/Bass Buster. He cannot dismantle himself across the screen to attack. Instead, he stands in place and throws parts of his body at the player. Like the previous version, the coating must be removed, but only the Mega Buster/Bass Buster will be available for the first battle. Unlike other bosses, the Green Devil will always reappear if the player return to the museum stage, and Remote Mine can defeat him in one shot.

Wily Machine 8 is a boss from Mega Man 8. Throw Water Balloons or slash the Flame Sword at Wily's window. Astro Crush is also useful as it grants Mega Man invincibility while the attack is in effect. When he is about to deploy the big laser, shoot the mouth with your Mega Buster to get him to withdraw it back. Watch out for the wheel as well. Sometimes it comes out as a saw blade that either rolls or bounces toward you, other times its a spinning gun. Once the first form is destroyed, he goes into the Wily Capsule. Flame Sword does the most damage to the Wily Capsule, but Flash Bomb is easier to hit him with. See Wily Capsule to know what his tactics are.

This Wily Machine also came equipped with an exceedingly powerful Evil Energy cannon when it first appeared, which nearly destroyed Mega Man in one hit. However, Duo flew in out of nowhere to destroy the cannon, weakening both him and the machine, allowing Mega Man to defeat it.