Black Zero

Black Zero (ブラックゼロ)', also known as ??? in Mega Man X8, is an upgrade for Zero that appears in most of the Mega Man X series games. It is similar to the Ultimate Armor in that it is usually accessible by a secret code, save for Mega Man X: Command Mission where it is used as his Hyper Mode. Except for Command Mission, this armor is never actually named in-game, and cannot be unequipped in Mega Man X4-X6 once received.

Characteristics
The effects of the Black Zero enhancement are not consistent throughout the games it appears in. In its first appearance in X4, it appears to be just a facelift. In X5 and X6, it enhances Zero's defense and saber power, it also adds 50% to Zero's weapon energy, like all of X's armors in these games do. However, three power-up parts will be automatically added for black armor in both games if he has them. In X8, it doubles Zero's dash speed and distance, doubles the damage power of his weapons, but halves his defense. This is Zero's only "armor" in those games, and considerably increases his already great power. For Command Mission, it doubles his attack power, increases his speed by 1.5, bumps up his WE gain per turn by 25% and cuts his fire damage to 75%, but has an extremely short number of usable turns without using Build Hypers.

Unlocking
Refer to the table below for codes used to gain use of Black Zero. The codes are listed with the button pressed and the number of times pressed next to it. In Mega Man X4 and X5, highlight Zero on the Character Select screen and enter the codes. In Mega Man X6 and X8, highlight Game Start, complete the sequence of buttons, and press Start.


 * In Mega Man X5, there is a way to receive the Black Zero enhancement without using a code. In the third Zero Space stage, there is a vertical shaft that leads to a capsule. Enter the capsule as Zero to enhance him into Black Zero (alternately, X can enter a similar capsule in the same area to obtain his Ultimate Armor). According to the conversation that Zero has with Dr. Light, he (Light) says he wasn't able to create any armor for Zero, but he is able to enhance his abilities. Zero is welcome to either take it or leave it, though Zero claims he doesn't need any upgrades. The Black Zero's enhanced saber can destroy energy shots (even Ultimate Armor X's Charge Shot).
 * In Mega Man X8, the player must redeemed all of Zero's available power-up chips and complete the game to save into a New Game Plus, by which the final power-up chip will be made available (Sigma Blade). Once that final power-up chip is redeemed, Black Zero will be made available immediately for selection. Black Zero will show up as "???" in the character selection screen when made available. But unlike previous games where Black Zero will override the Normal Zero, this game can still allow the player to select Normal Zero even if Black Zero has been unlocked. This method is the only method available for the PC version of the game where pressing codes on the title screen will not work.

Fake Zero
"Sigma, you should have studied the blueprints closer! There is only one Zero!"

- Zero, after destroying his copy

The armor is most likely a reference to the fake Zero in Mega Man X2, where if all three Zero Parts are collected by X, a Zero with black-hued armor created by Sigma appears in the last stage, and Sigma tries to convince X that he is the real Zero. The fake Zero is destroyed by the real Zero shortly after his appearance. If the game is completed without collecting all of Zero's parts, a black Zero will appear after the credits and reveal the Capcom logo. The false Zero also had a brief appearance in Mega Man X5's opening scene. 

Other media
In the Rockman X2 manga, Zero's armor becomes black when he is influenced by the Sigma Chip in his forehead, increasing his strength but making him a Maverick.

Merchandise
Bandai released two different model kits for the black armor as part of its Mega Armor model kit series. The first kit that was released featured Zero with pink upper arms and thighs, and purple hair, buster, and Z-Saber. The kit was later re-released and instead featured grey limbs and brown hair, buster, and saber. 

Trivia

 * A form similar to the Black Zero upgrade appears in Mega Man Zero 2, called the Proto Form. Both have black color schemes, and both have similar effects when equipped.
 * In Marvel vs. Capcom 3, when Zero is facing himself he will say, "Another soulless copy," which is most likely a reference to the Fake Zero.
 * In Mega Man X6, the Black Zero enhancement was intended to be accessible without use of the code by defeating the Zero Nightmare when it is at level 4. However because of design oversight this isn't possible as bosses will only be at level 4 when the PA rank is achieved which requires 5000 Nightmare Souls. As one way to unlock the endgame is to collect 3000 Nightmare Souls and since unlocking the endgame prevents the player from fighting Zero Nightmare and High Max if they have not yet done so, obtaining the Black Zero enhancement without the use of codes in Mega Man X6 is thus impossible. Despite this design oversight, the Black Zero enhancement is still coded to be rewarded to players that beat Zero Nightmare when it is at level 4. This can be achieved through cheating devices such as GameShark. It is worth noting that there is no special text or notification if the player achieves the enhancement through this method.
 * Zero was originally going to have his own Ultimate Armor instead of the Black Zero cosmetic change in X4. The reasons for it's removal are unknown.