Mega Man X4

Mega Man X4, known as Rockman X4 in Japan, is the fourth game from the Mega Man X series. It was the second game in the series to be released on the PlayStation and Sega Saturn (although it is the first original game; Mega Man X3 was ported to the systems), released in 1997 (and also re-released onto PlayStation as part of its greatest hits in 2002). It was later ported to the PC in 1998 and then re-released as part of the Mega Man X Collection. It was released on the Playstation Network in North America as part of the PSOne classics on September 2 2014.

Story
In the year 21XX, two large Reploid armies currently exist to counter the Mavericks: The Maverick Hunters and the Repliforce. The two organizations cooperated on several occasions, and during this time Zero befriended Colonel and Iris of Repliforce.

But one day, the aerial city Sky Lagoon was attacked by Mavericks, who sabotaged its power generator, causing it to fall to the city below, killing thousands. As Repliforce was present in the area, they were put under suspicion and Colonel was asked that Repliforce surrender for questioning. Having great pride, Colonel refuses and leaves with his sister. Their leader, General, is indignant of the suspicion and starts a coup d'état to build a Reploid-only nation. Although General says they only want to live in peace, not wanting harm for the humans, the entire Repliforce is considered Mavericks, and the Maverick Hunters are sent to stop them, starting the Great Repliforce War. Little do they realize that behind the scenes, a mysterious cloaked figure pitted them against each other, in a bid to wipe out both sides. During the war, Iris assists Zero while X is assisted by the rookie Double. After defeating several members of Repliforce, the Hunters fight Colonel and defeat him. Repliforce travels into space to begin their nation, and the Hunters chase after their satellite/space station. When playing as Zero, Iris is angered by her brother's death and fights him. The battle leaves her mortally wounded and she dies in Zero's arms. As X, it's revealed that Double was a spy of the cloaked figure and the two fight, resulting in Double's death; but not before insulting X for his naivety. The Hunters finally reach General and a battle ensues that leaves him severely wounded. Suddenly, the weapon in the station prepares to destroy Earth, and the cloaked figure is revealed to be Sigma. Sigma is destroyed by the Hunters, but the weapon can't be stopped by them. General sacrifices himself to stop the weapon, and the station explodes.

Gameplay
Mega Man X4 follows its predecessors as the player must combat Mavericks while traversing through obstacles and terrain. This is the second game to feature Zero as a selectable playable character, but the first game to feature him as a fully playable character (he had limited playability in the previous game). Unlike future games, players must play the entire game with the character they've chosen.

The playing styles of both characters differ from each other, giving the gamer a rather varied experience. Mega Man X still copies weapons through defeating bosses, utilizing the long range X-Buster. Zero however, learns techniques, which mimics an attack used by a boss, often with the use of his close-ranger Z-Saber, but none of these except his Giga Attack use Weapon Energy. Because of their gameplay differences, X is often recommended for novice to intermediate players since he can fight enemies from a distance while Zero is used for advanced players as he needs to get up and close to his targets.

The game is also the first to have actual multiple Armors in the game, as well as an "Armor" for Zero. X can find pieces for the Fourth Armor like he would any other armor in the previous games, enhancing his abilities further.

Finally, Mega Man X4 is the first X game to use cheat codes which unlock armors specific for the character selected. For X, he unlocks the Ultimate Armor (an enhanced version of the Fourth Armor), which first starts out replacing X's cyan colors with purple. When X visits any of the Light Capsules, he is automatically equipped with the full Ultimate set, giving him a Plasma Shot upgrade and the Nova Strike Giga Attack as well as enhanced defense and the ability to hover in the air (these abilities were also featured in the Fourth Armor, although the latter's use of the Nova Strike is limited). Zero on the other hand gets the Zero Armor, which gives him a black sheen and platinum blond hair, but does not affect his abilities in the least. The codes for unlocking these armors differ on the consoles.

Bosses
Eight Mavericks:

Others: 
 * Eregion
 * Colonel
 * Double (If X)/Iris (If Zero)
 * General
 * Sigma

Armors
X's Armors:
 * Standard Armor: X begins the game with this armor.
 * Fourth Armor: An all-around armor.
 * Ultimate Armor: Obtained by visiting any Armor Capsule after the use of a code. Allows infinite Nova Strikes.

Zero's Armors:
 * Red Armor: Zero begins the game with this armor.
 * Black Zero: Replaces the Red Armor through the use of a code. Cosmetic change only.

Trivia

 * Like Mega Man 8, X4 has been a target of ridicule due to its sub-par voice-acting, including X being voiced by the same actress who portrayed Mega Man in 8, which received similar criticism.
 * It is not known which ending in this game is canon: X's or Zero's. This stems from the fact that both Zero's battle with Colonel and X's battle with General are referenced by The Skiver in Mega Man X5, and also images of Zero battling Colonel and X fighting Double in the opening. It is most likely a combination of both endings.
 * Some of the Special Weapons in this game are re-used in the battle between X and Zero (if the player chose Zero) in Mega Man X5. The Special Weapons in question are Soul Body, Double Cyclone and Frost Tower.
 * This is the first game to show official names for an armor; ironically, it is for the secret Ultimate Armor.
 * It should be noted that this is the debut of the Ultimate Armor and Black Zero as unlockables.
 * Although there are two more games in the X series in which the Final Boss is fought in three battles (Mega Man X and Mega Man X8), X4 is the only game where the player fights Sigma in all three phases.
 * X4 is also the only game in which Sigma uses two forms alternately in one battle, which is the case for the final phase of the boss battle.
 * X expresses fear in the ending that he himself may become Maverick. He requests to Zero that, should he ever exhibit symptoms of him becoming a Maverick, that he is to "take care of him".
 * The ending monologue in X's story also seems to implicate foreshadowing that he may become a Maverick in the future as well, hinting his original intended role in the first Mega Man Zero game, which was changed to be Copy X.
 * Chill Penguin and Blizzard Buffalo make cameo appearances in the background of Frost Walrus' stage. Buffalo was killed and frozen by Frost Walrus in Yoshihiro Iwamoto's Rockman X4 manga.
 * This game marks the first time that a "Warning" signal is used when a Boss is about to be fought.
 * On a few occasions, the game may become stuck on a "Warning" signal on the PlayStation version, forcing the player to have to reset the game. This glitch also occurs in Mega Man X5.
 * Unlike its original series counterpart, Mega Man 8, this game was built for the PlayStation - the Sega Saturn version is a direct port and features no additions over the original version. In fact, many of the special effects were not optimized for the Saturn and are dithered on it. The only enhancements to this otherwise downgraded port is true looping to the music (meaning it doesn't fade out or stop and replay from the beginning), as well as some adjustments to the Frost Walrus stage music and the boss music for the intro stage (adding a crescendo). Finally, there is a new "heat wave" effect in the background of the second half of the intro stage and Magma Dragoon's domain.
 * On the PC version, the music for the final battle with Sigma was switched around. In other words, the music that played for the first phase of the battle on the PSX and Saturn versions became the final phase in the PC version and vice-versa. This can be easily fixed, if one goes into the game's "BGM" folder, and swaps the names of "BGM01.SE" and "BGM02.SE" around. In fact, the game uses regular wave audio files (renamed with a ".SE" extension), so, any music that the player wants to hear can be placed anywhere throughout the game, as long as it's in .wav format, by simply renaming any desired wav files with the appropriate BGMXX.SE title and placing it in the BGM folder, making sure to back up the original files. Mega Man X5 on the PC works in the same manner.
 * X's eyes appear blue in the anime cutscenes, where canonically they are green. On the flip side, Zero's eyes are green in the cutscenes while they are canonically blue for the most part.
 * The majority of the in-battle voice acting for the eight Maverick bosses was cut from the English language releases.
 * This game was the first in the series to utilize a dialogue sequence between the Hunters and the Mavericks instead of going straight to the battle. This would carry on for the rest of the series.
 * In the 1st Sigma battle during "Round 2", it is possible to stand right behind Sigma as he uses his eye lasers on the floor, allowing a number of free hits until the attack ends. This is easier to attempt as Zero.
 * The crossover game Project X Zone features X and Zero as playable allies. Some of their Special Weapons and techniques are from Mega Man X4, namely Frost Tower and Twin Slasher for X and Kuuenbu, Hyouretsuzan and Raijingeki for Zero. Certain events in Project X Zone suggest that the game's plot occurred some months after the Repliforce incident.
 * In this game, only three of the eight stage bosses are actual virus-infected Mavericks, as their health bars display Sigma's symbol on their bottom instead of the Repliforce emblem. They are Magma Dragoon, Split Mushroom and Cyber Peacock. The other five, as well as the rest of the Repliforce, are just revolting for having been deemed mavericks.
 * Mini-bosses have their own health bar in this game.