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.

Dust Man is a Robot Master with a built in vacuum cleaner, originally created by Doctor Mikhail Cossack to be used for sanitation, being able to inhale various types of garbage. His powerful suction power got Dr. Wily's attention and he was modified into a combat robot, and fights against Mega Man in Mega Man 4. Dust Man's main weapon is Dust Crusher, a large piece of scrap metal that launches shrapnel in several directions. He can also pull opponents towards himself with his vacuum.

Skull Man is a Robot Master created specially for combat with balanced offense and defense by Dr. Cossack while he was working for Dr. Wily in Mega Man 4. He attacks with shots from his arm cannon, and can generate a skull-shaped energy shield called the Skull Barrier for protection. Skull Man only moves or attacks when Mega Man does the same; however, he doesn't move if Mega Man only jumps.

Dive Man is an aquatic-themed Robot Master based off a submarine. Dive Man was created by Dr. Cossack for deep sea exploration. When modified for combat by Dr. Wily however, he gained the ability to launch special homing torpedoes from his chest that can utilize two different propulsion systems - screw propulsion for underwater usage and jet propulsion for land. Due to a design error, Dive Man can also attack by launching himself forward like a torpedo, crashing into his foes to do major damage. Ironically, although he is an aquatic robot, he can get motion sickness.

Drill Man was created by Dr. Cossack for underground construction and mining until he was reprogrammed to be a combat robot by Dr. Wily in Mega Man 4. His main weapon, the Drill Bomb, is intended to pierce dense objects and explode, causing as much damage to the object as possible. Like Crash Man and Spark Man, Drill Man has no hands. Instead, he has two powerful, all purpose drills made for grinding through solid rock and dirt, which he incorporates into his attacking strategy.

Mothraya is a giant robotic moth, and is the boss of Cossack Stage 1 in Mega Man 4. The red flashing light is its weak point, and Ring Boomerang is the best weapon to use (though Drill Bomb and Dust Crusher are also good options). It can thrust its spike-tipped "proboscis" into the floor, causing a part of the floor to be destroyed.

Square Machine is a room-like boss, which appears at the end of Cossack Stage 2 in Mega Man 4. It slides like a sliding slot game, doing this at various speeds. At its slowest speed is when it will merge together and Mega Man will need to get inside it to attack it. When it is fully formed, its weak spot, the large flashing red light, will appear. Its weakness is Dust Crusher, although the Wire Adapter can be used as well. Mega Man will have to ride the platforms and dodge the shots as he attacks. It is sort of a bigger and 3-part Picopico-Master.

Cockroach Twin is the name of the two boss enemies at the end of Cossack Stage 3 in Mega Man 4, fought one at a time. The first one stays on the ceiling, and the second walks around the whole room in a clockwise pattern. The room has spikes on the bottom, so the player must be careful when jumping. Drill Bomb and charged Pharaoh Shot are the best options against them.

Dr. Mikhail Sergeyevich Cossack, rus. Михаил Сергеевич Казак is a Russian robotics engineer member of the Stravinsky Science Academy, and lives with his daughter, Kalinka. In Mega Man 4, he sent a letter to Dr. Light stating that he has created eight Robot Masters (consisting of Bright Man, Dive Man, Dust Man, Drill Man, Pharaoh Man, Ring Man, Skull Man, and Toad Man) and sent them to take over the world, in order to show the world his genius. Mega Man set out to defeat the eight new Robot Masters, and made his way to Cossack's Siberian fortress. Just as he defeated Cossack, Proto Man appeared with Kalinka and revealed the truth: Dr. Wily had kidnapped Kalinka and forced Dr. Cossack to build the robots as ransom. After Mega Man defeated Wily once again, Dr. Cossack built a robotic bird called Beat for him, as a gift for saving his daughter.

Metall Daddy is the first boss of the Wily Castle in Mega Man 4. This Met can jump to where Mega Man stands, and when it lands, it makes four normal Mets fall from the top of the screen. It is weak to Ring Boomerang and Dust Crusher. The Powmettaur from Mega Man ZX is similar to this Met.

Tako Trash is the boss of the second Wily Stage of Mega Man 4. It sends out large exploding balls and spits flames. The green light on its forehead is its weak spot, and the best weapon to use is Ring Boomerang.

Wily Machine is the name of the machines that Dr. Wily uses in the end of most games from the original Mega Man series. Most of them have Wily's flying saucer on them and have two forms of attack, with the second form's weak point being the cockpit and Dr. Wily himself. Starting with Mega Man 4, the Wily Machines have been followed up by an escape pod, named the Wily Capsule. Also, starting with Mega Man 4, Wily's Machines have had an unmistakable skull motif.

Wily Capsule is the teleporting escape pod that Dr. Wily rides and uses for combat after the destruction of his Wily Machine. First appearing in Mega Man 4, it is the final form of Wily in said game and onward, which torments Mega Man for the rest of the classic series. It was at its strongest in Mega Man 7. The version in Mega Man 5 is called Wily Capsule II, and in Mega Man 8 it's called Wily Capsule Great. In other appearances it is referred to simply as "Wily Capsule".