Dr. Cossack's Citadel

Dr. Cossack's Citadel, also known as Cossack Castle (コサック城), is Dr. Cossack's fortress in Mega Man 4. After the defeat of all eight Robot Masters, Mega Man must go through the castle, which consists of four stages. Mega Man fights against the bosses Mothraya, Square Machine, Cockroach Twins and Dr. Cossack inside the Cossack Catcher. After Dr. Cossack's defeat, Proto Man appears with Cossack's daughter, Kalinka, and it's revealed that Dr. Wily captured Kalinka to force Dr. Cossack to work for him.

Other appearances
Dr. Cossack's Citadel also appeared in the Game Gear Mega Man. Although the beginning of the final stages shows the Wily Castle from Mega Man 4, the ending shows Cossack's Citadel exploding instead, being possibly a mistake from the game.

In the manga Mega Man Megamix, the citadel is the home of Dr. Cossack's family. However, during the Return of the God of Death story arc, it is destroyed by Skull Man (Clad in a black cloak and scythe, resembling a Grim Reaper) and Reggae leading an army of Skeleton Joes into the Citadel, kidnapping Dust Man, Pharaoh Man and Drill Man in the process.

Cossack Stage 1
The first stage of Dr. Cossack's Citadel. Mega Man begins outside in snow and makes his way up the walls of the citadel as it begins to start snowing.

Enemies:
 * Jumbig
 * Ladder Press
 * Mono-Roader
 * Skeleton Joe
 * Tom Boy
 * Togehero
 * Up'n'Down
 * Boss: Mothraya

Cossack Stage 2
The second stage is set inside the citadel and has a long area full of spikes that Mega can only be crossed by Rush Jet. There are also small square platforms that must be carefully crossed, because they have spikes on them that can change sides.

Enemies:
 * Battonton
 * Docron
 * Garyoby
 * Ladder Press
 * Minoan
 * Mono-Roader
 * Togehero
 * Boss: Square Machine

Cossack Stage 3
The third stage takes place in the clouds above the citadel in daylight and is full of platforms that appear out of nowhere. Be careful when stepping on them, as they fall under your weight and will then float up, up and away when you jump off them.

Enemies:
 * Biree
 * Garyoby
 * Jumbig
 * Pakatto 24
 * Ring Ring
 * Togehero
 * Boss: Cockroach Twins

Cossack Stage 4
The last stage. The action returns to the citadel, now at night. At one point, the path splits in two, and you have the choice of either taking the upper route or the lower route. However, the lower passage is blocked by a wall that can only be opened up by blasting it with a Drill Bomb, and in order to reach the wall, you must use the Wire to attach to the ceiling.

Enemies:
 * Biree
 * Battonton
 * Docron
 * Helipon
 * Jumbig
 * Pakatto 24
 * Shield Attacker
 * Tom Boy
 * Up'n'Down
 * Boss: Cossack Catcher