Mega Man 4

Mega Man 4, known in Japan as Rockman 4: A New Evil Ambition! (ロックマン4 新たなる野望！！), is the fourth game in the Mega Man series released for the Famicom and NES late in the console's life (1991-93). The game introduced the New Mega Buster as well as the concept of a "fake" villain (Dr. Cossack).

Overview
Mega Man 4 was the first game in which it was not known that Dr. Wily was the villain, using a new antagonist until the end, Dr. Cossack. The game also introduced the New Mega Buster, an upgraded version of Mega Man's Mega Buster. This upgrade allows him to charge his shots for more damage. Eddie, a robot that gives Mega Man a random item, was also introduced.

A New Villain
A year after Gamma's defeat in Mega Man 3, many thought Dr. Wily was dead after he was crushed in the last game, and the world had been living in peace so far. However, Dr. Light received a message from a mysterious Russian scientist named Dr. Cossack, claiming to be the greatest scientific genius in the world and having been far too long overlooked, and sent eight of his strongest robots to destroy Mega Man and prove he is better than Dr. Light:

From the instruction manual:


 * Good Evening, Dr. Light. Allow me to introduce myself - I am Dr. Cossack. You may not have heard of me, but soon the world will know my name.


 * Over the years, you have been hailed as the greatest robot designer in the world, while my robotic creations have been totally ignored. I cannot allow this to continue. The world must be made aware of my genius!


 * From my Siberian citadel, I've sent eight of my most powerful robots to destroy that titanium troublemaker, Mega Man. Once they have obliterated him, I will place his broken body on display for the entire world to see. Only then will I be allowed to take my place as the greatest robot designer of all time!


 * Dr. Cossack

Cossack's army of robots began to make their move, so Mega Man went after Cossack with his New Mega Buster.

After defeating the robots and Dr. Cossack, Mega Man discovers that Cossack's daughter Kalinka had been kidnapped by Dr. Wily (who was very much alive and, it appears, hiding in Russia) to make Cossack work for him, but luckily Proto Man betrays Wily and rescues her. Mega Man heads to Wily's citadel and defeats him once more.

Fortress Bosses
Dr. Cossack's Citadel:
 * 1) Mothraya
 * 2) Square Machine
 * 3) Cockroach Twins
 * 4) Cossack Catcher

Wily Castle:
 * 1) Metall Daddy
 * 2) Tako Trash
 * 3) Rematch with the Robot Masters and Wily Machine 4
 * 4) Wily Capsule

Trivia

 * The opening scene of the game shows Mega Man with blue hair, while the ending scene shows him with black hair. However, this might be due to color limitations with the sprites.


 * The Wily Machine in this game is the first of many to have the skull motif, a trend that is followed by all succeeding games' Wily Machines. This is also the first Mega Man game with the Wily Capsule as the final boss, which is used by Wily for the rest of the classic series.


 * This is the first game to feature a unique music track for the game's last boss.


 * Of all the classic Mega Man games, Mega Man 4 takes the longest time to fill the health meters for Mega Man and his enemies.


 * This is the first time Mega Man can charge his buster due to the addition of the New Mega Buster.


 * This is the first game where Dr. Wily tried disguising his intentions by making it seem as if someone else is behind everything.


 * This is the only game in the series to feature two water-themed Robot Masters: Dive Man and Toad Man.


 * Interestingly, when Dr. Wily appears after Mega Man destroys Dr. Cossack's machine, he teleports into the room, much like Mega Man and Proto Man, using Proto Man's teleporting sprite.


 * If the player looks closely when Mega Man is getting a weapon, at some part of the sequence, Mega Man's eyes turn orange instead of staying blue.


 * The eight winners of the character contest from this game received a golden copy of Rockman 4.


 * It is possible for Mega Man to "kill" Dr. Wily after Wily escapes from his Wily Machine No. 4 in his escape pod by using the Rain Flush as seen in the video above. However, doing this will result in Mega Man getting stuck in Wily's chamber and the player having to reset the game.


 * Four of the Robot Masters share the same intro pose. These four are Toad Man, Bright Man, Ring Man, and Skull Man.


 * The theme that plays during the credits is a remake of part of the Mega Man 2 opening.


 * This is the first Mega Man game to have an introduction story with cut scenes.


 * This is the first Mega Man game with two boss castles, Dr. Cossack's and Dr. Wily's.


 * This is the first Mega Man game since the original where players can revisit Robot Master's levels.


 * This is the first Mega Man game to feature "hidden" paths that can be taken to acquire special abilities.


 * This is one of the four Mega Man games to have a fake final boss, the others being Mega Man 5, Mega Man 6, and Mega Man & Bass.


 * A possible reason why this game's setting took place in Russia, and introduced a Russian antagonist was because the year this game was released was the same year as the fall of the Soviet Union and the Berlin Wall. This probably green-lighted the idea of using Russian characters this time around.
 * Proto Man's whistle is missing when he appears after rescuing Kalinka.
 * There were a total of 70,000 boss character submissions for this game.