Full-screen attacks

The Giga Attack (ギガアタック) is a powerful attack that can be used by X's armors. The most common version is the Giga Crash (ギガクラッシュ), a full-screen attack that damages or destroys all enemies seen on-screen. It first appeared in Mega Man X2 as the ability of the armor's body part, and appeared in all subsequent games after Mega Man X3.

The Giga Attack is not limited to X, however. Zero can also use his own versions of Giga Attack, as Command Arts learned from defeated bosses from Mega Man X4 onwards (and also Mega Man Xtreme 2). His versions of the attack more closely resembles the original incarnations performed by some of X's armors.

Mega Man X2 and Mega Man Xtreme2

 * X: The armor from Mega Man X2 and Mega Man Xtreme 2 are the same, so the same Giga Attack is available. This is the first Giga Attack to be re-used for a future game. To be used, it requires a full weapon gauge, and usually the best way to charge it up is to deliberately take damage from projectiles.
 * Zero:

Mega Man X4

 * X: The Fourth Armor and the Ultimate Armor, both introduced in this game, can perform the powerful Nova Strike, a fast flying dash that destroys most normal enemies in its path. Although classified as a Giga Attack, it's the first in the series not to be a full-screen attack. It's also the most recurring Giga Attack in the series, since the Ultimate Armor appears in all subsequent games after X4 (with the exception of X7).
 * Zero:

Mega Man X5

 * X: Unlike the two armors from the previous game, the Falcon Armor's Giga Attack closely resembles the original. The Gaea Armor, however, stands out as having the shortest range for a Giga Attack in the entire series.
 * Zero:

Mega Man X6

 * X: Both Giga Attacks of the Blade Armor and Shadow Armor have limited range, since both involve the use of the Z-Saber. The former uses an upgraded Z-Saber slash (which can send energy waves forward), while the latter uses the Z-Saber to summon two large crescents to spin over and under X.
 * Zero:

Mega Man X7

 * X: The Glide Armor possesses a similar full-screen Giga Crash attack like that of the first Giga Crash and the Falcon Armor.
 * Zero:

Mega Man X8

 * X: For the first time, the Giga Attack has been replaced by the "Giga Ability" which is only made possible when all four component parts of the same color are used in the Neutral Armor (namely the Icarus Parts and the Hermes Parts, which will bestow the name of the respective Armors together with the respective Giga Ability).
 * The Icarus Armor's Giga Ability is the "Giga Crash" which works the same way as the "Giga Crush" attacks used by X in Mega Man X2 and X7, with the difference of the energy being able to refill itself just by being active in the mission (switching out during gameplay will halt the recharge until X is switched back) and also being able to use the attack even when the energy isn't completely refilled with a reduced destructive power and range. This is different from the previous Giga Crush attacks where a full weapon meter is required and X has to take damage to fill up the weapon gauge used for this attack.
 * The Hermes Armor's Giga Ability is the "X-Drive" which powers-up X's existing Hermes Armor capabilities. When it is activated, a blue-colored energy field surrounds X and each of his Hermes Parts are given a boost in abilities on top of the normal Hermes Armor capabilities: Head Parts H grants X the ability to charge his buster two times faster than normal; Body Parts H grants X double invincibility time whenever X gets hit by attacks; Buster (Arm) Parts H grants X a fourth-level Charge Shot which fires a 5-way shot; and Foot Parts H grants X double movement and dash speed. When the X-Drive is in effect, the energy inside the gauge that uses this will drain and the effect wears off when all the energy used is depleted, in which it will also refill itself for successive usage. However, using the ability when the energy isn't completely filled will result in a shortened effect duration. The effect and recharge will also be halted if X is switched out during gameplay.
 * Zero:

Other Appearances

 * In the non-canon scenario of Mega Man X2 (where X fight Zero before facing Sigma), Zero uses his Earth Gaizer Giga Attack.
 * If you select X in the third fortress stage in Mega Man X5, when fighting Zero he uses versions of his Giga Attack, Messenko (the Japanese name for C-Flasher) and Shin-Messenko. However, these attacks are different from the actual C-Flasher attack Zero learns in the same game.
 * Copy X's first form uses an angelic armor; he also uses an air dash attack that is slightly similar to the Nova Strike.
 * The last form of Omega (Zero form), the final boss of Mega Man Zero 3, uses weaker, modified variations of Zero's Rakuhouha and Rekkoha. Also, Omega's Kuenzan projects crescents in an arc similar to his version of Rakuhouha.
 * In the commercial for the first Rockman Zero game, Zero was shown creating a powerful explosion after being awakened. The explosion destroyed all enemies, leaving Zero standing strong, which might be a reference to a Giga Attack.
 * Mega Man Model A uses a Giga Crush as its special ability.
 * OVER-1 is able to use a Giga Crush that destroys all on-screen enemies. He continues moving forward steadily while executing the attack, and then must wait for a cooldown before using it again.

Trivia

 * Although Axl doesn't receive a Giga Attack/Ability, some of the attacks he can use while transforming into some Mega Man X: Command Mission boss(es) (ex: Silver Horn, Mach Jentra, Rafflesian, Incentas) can hit all enemies at once.
 * Ironically, Model A Biometal from Mega Man ZX Advent, has a Giga Attack, marking the chronological return of the attack to a playable character since Mega Man X8 (although a secret character from Mega Man ZX has the same ability as the character it's based on).