Toad Man is a Robot Master that was created by Doctor Mikhail Cossack. Like any frog, Toad Man jumps like there is no tomorrow. His weapon, the Rain Flush, can damage Mega Man regardless of where he is.

Bright Man is a Robot Master that was created by Doctor Mikhail Cossack to act as a light source on dark expeditions. The light bulb on his head is capable of emitting one million watts of power. Dr. Wily reprogrammed him in Mega Man 4 to serve as a combat robot. His main weapon, the Flash Stopper, stuns and blinds opponents with an intense burst of light for a brief moment.

Pharaoh Man is a Robot Master designed as a pharaoh that resembles Tutankhamun. He was originally created by Dr. Cossack to explore pyramids, but was modified for battle by Dr. Wily in Mega Man 4. He is a charismatic leader, said to have over 1000 Mummira working for him, but becomes timid near beautiful women. He was created with high resistance and agility to avoid traps in pyramids and has very sensitive eyes to be able to see in dark places, but this also makes him weak to strong lights like the Flash Stopper, which could blind him easily. His main weapon is the Pharaoh Shot, a thermal sphere that can be charged with solar energy.

Ring Man is a combat Robot Master that was created by Doctor Mikhail Cossack specifically to terminate Mega Man in Mega Man 4. Ring Man is a great strategist and is confident in his abilities. His main weapon is the Ring Boomerang, a ring-shaped boomerang with high penetration power that can be thrown at any angle and can travel any distance.

This unnamed boss, known by nicknames such as "Parabola Gun" and "Satellite Cannon" due to its parabolic antennae shape, is a boss from Mega Man IV. After the defeat of the four Robot Masters from Mega Man 4, Mega Man follows Dr. Wily and is attacked by the defenses of his Wily Station. Mega Man attacks the base and fights against this cannon in the top of the fortress.

This cannon attacks by releasing one (two after losing half of its energy) spinning projectiles from the core. It also throws the core to the top of the screen, which homes on Mega Man's direction and than returns by rolling in the ground. When it throws the core, it's safer to dodge it by sliding to the right when it moves on Mega Man's direction. It can only be damaged when the core opens to attack with the spinning projectiles, being vulnerable to Pharaoh Shot. After defeating this boss, Mega Man enters the fortress and fights against Ballade.

The third and final robot in the Mega Man Killer series, Ballade has a great sense of pride and desires to be nothing but the strongest, and dislikes weak opponents. Does Ballade remind you of someone else? He should. These very traits would later be passed down to Bass. You might think Ballade is a quickster with a headpiece very similar to Quick Man, but in truth, Ballade has about average speed and his Ballade Cracker is easy enough to dodge. While Ballade is similar to Bass, there is one key difference between the two: Ballade knows how to show some humility. After his second loss to Mega Man, Ballade, in a surprising show of character development admits that he was wrong and helps Mega Man escape Wily's fortress by blowing himself up, destroying the final barrier that was preventing the Blue Bomber escaping. Why Green Biker Dude has a bigger fan following than Ballade, I'll never know.

Stone Man is a strong Robot Master that was built by Doctor Albert Wily to look like and be as tough as a bunch of bricks. He also bears a striking resemblance to his friend Guts Man.

Charge Man is a Robot Master based on a steam locomotive, which is used by him as camouflage to make shipments to Dr. Wily. He is unique in that he is powered by coal and water, lowering his operating costs exponentially. His main attack, the Charge Kick, makes him throw a full-throttle kick at his maximum speed. He's also able to launch flaming pieces of coal from his smokestack.

Napalm Man is a Robot Master created by Dr. Wily to protect his secret weapons factory, where he would spend his spare time collecting and searching for weapons as strong or stronger than his own.

Napalm Man is a weapons enthusiast equipped with an array of explosive weapons all over his body - he is equipped with missiles and Napalm Bomb launchers in his arms, he can fire missiles from his head and also launch six small homing missiles from his shoulders. He has treads on his feet and can increase his speed with a rocket on his back.

Because he is generally considered to be a walking weapon, even his allies feel uncomfortable near him, so he doesn't have many friends.

Crystal Man is a mysterious Robot Master that was created by Dr. Wily to help finance his operations through the creation of artificial crystals, which Crystal Man can also use as a weapon called the Crystal Eye by releasing crystal orbs that rebound off surfaces. He can also attack with energy shots from the crystal in his abdomen.

Ballade is the third and last "Mega Man Killer" robot built by Dr. Wily. Ballade has great pride and believes he is the strongest robot, but after losing twice to Mega Man, he realizes his mistake and sacrifices his life to save Mega Man in the end of Mega Man IV, by self-destructing to open the way for Mega Man from Dr. Wily's station. Ballade attacks with a powerful explosive called the Ballade Cracker, and has a second form that increases his strength.

This unnamed boss, most known by the nicknames "Bridge" and "Defense System", is the first boss of the Wily Battleship in Mega Man IV. It attacks with an extendable arm and the core can use special weapons from Robot Masters, varying between Ballade Cracker, Ring Boomerang, Power Stone and Napalm Bomb. It can only be damaged when the core is open. It's most vulnerable to Beat, but if the player wasn't able to obtain him, Ballade Cracker can also deal a good amount of damage.

Hunter is the name of two sub-bosses from Dr. Wily's space station in Mega Man IV. They are modified versions of the Octopus Battery.

The first Hunter bounces diagonally throughout the room and creates duplicates of itself when damaged. The second Hunter spins along the surfaces of the room followed by one copy and shoots at Mega Man.

Wily Robo Iron Golem is a giant robot that plays the role of Wily Machine for the fourth Game Boy game. It is an improved version of the Wily Machine in Mega Man: Dr. Wily's Revenge. Wily wanted to create a giant robot and began its development in his space fortress. The robot was still incomplete when Mega Man arrived, but is able to fight. It's so tall, Mega Man begins the fight by attacking a green gem located on its chest. The gem occasionally launches energy balls while the fists attempt to punch and crush Mega Man, making objects fall when he tries to crush him. The fists can be used to reach the gem and attack it. It's weak to Crystal Eye, but the player can use Power Stone or Rush Coil to reach the gem more easily.

After damaging the gem, it falls down and attacks with the head, which follows a set pattern of sucking Mega Man towards it with the mouth, firing energy bolts from its antennae and charging into Mega Man. The charge can be held back by repeatedly shooting the head. It can only be damaged when the mouth opens to suck Mega Man in. It is vulnerable to Ballade Cracker. After destroying the robot, Wily uses a Wily Capsule to attack.

The Wily Capsule used by Wily after the defeat of Wily Robo Iron Golem. While it could disappear and reappear like its previous incarnations, this one primarily attacked by dropping bombs on Mega Man, taking out sections of the floor. After dropping two bombs, he glides to the right and drops bouncing balls. Its weakness is the Pharaoh Shot. Ballade Cracker is also useful against him, as it can shoot in more directions.