Mega Man 4

Mega Man 4, known in Japan as Rockman 4, is a platform game developed by Capcom for the Nintendo Entertainment System. It is the fourth game in the original Mega Man series and was originally released in Japan on December 6, 1991. The game's story takes place after the third defeat and supposed death of Dr. Wily, and features the Earth coming under threat from a mysterious scientist named Dr. Cossack and his eight 'Robot Masters'. Fearing the worst, Dr. Light sends Mega Man to save the world once again. Mega Man 4 carries on the same action and platforming gameplay as the first three games, in which the player completes a series of stages in any order and adds the weapon of each stage's boss to Mega Man's arsenal. One notable added feature is the 'New Mega Buster' (often shortened to 'Mega Buster'), an upgraded arm cannon that lets the player charge a regular shot into a much more powerful blast. The development team was mindful that this innovation would change the overall feel of the game.

Mega Man 4 takes place in an unspecified year during the 21st century, described as the year '200X'. One year after the events of Mega Man 3 and the supposed demise of the evil Dr. Wily, Dr. Light receives a letter from a mysterious Russian scientist named Dr. Cossack claiming that he is the world's greatest robot engineer. Cossack states further that he will unleash his army of robots upon the world as a test for Light to see which of the two of them is the better inventor. Light calls upon his own greatest creation, the hero Mega Man, to go after Cossack's Robot Masters.

Upon defeating the eight Robot Masters—Toad Man, Bright Man, Pharaoh Man, Ring Man, Dust Man, Skull Man, Dive Man, and Drill Man—Mega Man makes his way to Cossack's icy fortress. However, in the middle of his battle with Cossack, Mega Man's brother Proto Man teleports in with Cossack's daughter, Kalinka. The girl begs Mega Man to stop fighting her father and elaborating that Dr. Wily had kidnapped her and forced her father into building an army of robots. With Wily's plan undone by Proto Man, he steps out of the shadows. Mega Man pursues his nemesis and fights through the newly built Skull Castle, but Wily manages to escape in the end. Mega Man escapes as the fortress begins to self-destruct, and rides home on the top of a passing train, where he is greeted by Roll and Rush.

Mega Man 4 features similar gameplay to the previous three games. The player must complete a series of eight stages in an order of the player's choosing. The protagonist, Mega Man, is able to run, jump, shoot, and climb his way past obstacles and enemies; the game also retains the slide ability which debuted in Mega Man 3. At the end of each stage is a Robot Master boss. Upon defeating a Robot Master, Mega Man gains the Robot Master's signature weapon, which can then be used by the player in subsequent stages. Once all eight Robot Masters are destroyed, two separate sets of linear stages must be completed to finish the game. One major addition to the gameplay in Mega Man 4 is the 'Mega Buster', an upgraded version of Mega Man's arm cannon. By holding down the firing button, the player can now charge a shot, resulting in a blast far more powerful than the standard shot. This feature was later used in subsequent incarnations of the franchise.

The hero's dog Rush makes a return from Mega Man 3 with the ability to transform into 'Coil', 'Jet', and 'Marine' modes for navigating different environments. Aside from Rush, two additional support items called the 'Wire Adaptor' and the 'Balloon Adaptor' also aid the player in reaching areas not normally accessible. However, these hidden adaptors must be found in the stages rather than being awarded for defeating a Robot Master. Like the Master Weapons, the three Rush modes and the two adaptors are each limited to an amount of weapon power that drains when in use. The character 'Flip Top' Eddie is introduced in Mega Man 4. Eddie, who went on to appear in later Mega Man games, provides the player with a random item (such as health or ammunition) at designated points in some of the levels.