Mega Man 4

The fourth game in the Mega Man series for the NES. It was released in Japan in December of 1991, closely followed by a North American release in January of 1992. PAL territories didn't get it until nearly a year later, in December of 1992. It has since seen numerous re-releases, including the Rockman Complete Works, Mega Man Anniversary Collection, Virtual Console, and PSN.

It had been about a year since the events of Mega Man 3. Dr. Wily had seemingly perished after the final battle, having been apparently crushed by the falling debris from his fortress. But the peace is short-lived when Dr. Light is contacted by a new Mad Scientist named Dr. Cossack, who has sent his own new breed of robot masters out to challenge Mega Man. Tired of Dr. Light receiving all of the recognition for his accomplishments while his have been ignored, Cossack intends to destroy Light's crowning achievement and then put his broken body on display for the whole world to see, as proof that he is the superior one.

However, once Mega Man had defeated Cossack's eight robot masters and confronted the doctor himself, it's revealed that Dr. Wily is still alive, and had kidnapped Dr. Cossack's daughter, Kalinka, and forced him to use his robots to battle his nemesis. Mega Man defeats Wily, who escapes, and peace is restored once more.

Tropes:

 * Auto-Scrolling Level: The third Cossack stage is one of these, a rarity in the series.
 * Barrier Warrior: Skull Man. You too, once you receive his Skull Barrier.
 * Behind the Black: Pharaoh Man's level. After the first part, you have to drop down a crevice to continue, but going forward nets you a special item.
 * Blackout Basement: Parts of Bright Man's level become this if you shoot the 100-Wattons that fly through the area.
 * Blinded by the Light: The Flash Stopper
 * Boss Arena Urgency: Mothraya destroys part of the floor with one of its attacks.
 * Build Like an Egyptian: Were you expecting Pharaoh Man's stage to be anything else?
 * Charged Attack: This is the first game that allows Mega Man to charge up his buster. The Pharaoh Shot is this too.
 * Cranium Ride: Bright Man's stage has you ride a robotic grasshopper over spikes on a few occasions. Pharaohman has a similar gimmick in his level.
 * Denial of Diagonal Attack: Averted by the Pharaoh Shot, which can be aimed diagonally; played straight with everything else.
 * Disc One Final Boss: Dr. Cossack
 * Down the Drain: Most of Toadman's stage and part of the first Wily level. Diveman's stage is either this or Underwater Base.
 * Dramatic Thunder: Cossack's Siberian Citadel is introduced this way.
 * Everything Makes a Mushroom: Dr. Wily's fortress makes a skull-shaped mushroom cloud when it goes up at the end.
 * Game Breaking Bug: It is possible to kill Dr. Wily as he's ejecting from his exploding Wily Machine if you fire the Rain Flush and time it just right, so the rain starts as he's flying out. However, doing this will mess up an Event Flag that ends the level, meaning you're stuck in that room, forcing you to reset.
 * Glorious Mother Russia: The Cossacks; Fanon has taken it Up to Eleven.
 * Hijacked By Wily
 * Homing Projectile: The Dive Missile.
 * I Have Your Daughter: How Wily got Cossack to do his bidding.
 * King Mook: The Met Daddy, the boss of the first Wily stage.
 * Ledge Bats: This game introduces Up 'n Downs, an annoying little enemy that hides in Bottomless Pits and jumps out just as you're jumping over them, and can easily knock you in if you're not expecting them. Nearly every game after this has a variation of these guys.
 * Quicksand Sucks: Part of Pharaoh Man's level involves this.
 * Renegade Russian: Subverted in the end; Dr. Cossack's actually a pretty decent guy.
 * Rings of Death: The Ring Boomerang.
 * Shout-Out: Mothraya, the first Boss of Cossack's Citadel.
 * Skele-Bot 9000: The Skeleton Joes that inhabit Skull Man's stage are this. They even reassemble if they're not totally destroyed by a Charged Attack.
 * Skull for a Head: Skull Man, obviously.
 * Super-Hero Origin: Mega Man's origin story had previously been All There in the Manual, but this game goes ahead and puts this in the game's intro.
 * Teleport Spam: This is the first game where you fight Wily in his teleporting saucer.
 * This Is a Drill: Drill Man, and by extension the Drill Bomb.