Model O

Model O (モデルO) is a Biometal from Mega Man ZX based on Omega.

History
Model O is a mysterious Biometal whose origin is unknown. It's believed it was created around the same time as the Model W's that formed from the pieces of Ragnarok. The data of Omega from Dr. Weil's memories probably formed Biometal Model O as a strange stone, presumably so because it was near the Model W core. Model O itself is shaped like the Greek letter, Omega (Ω). No official artwork of Biometal Model O is known to exist.

After defeating Omega (in his Zero form) or the eight bosses from the previous Mega Man Zero games in Area N, Vent/Aile obtained a Mysterious Rock. In the Guardian Base, Fleuve discovered that it's energy properties were similar enough to those of the other Biometal fragments for the character to Megamerge with it. Upon use, the player will instantly resemble Omega in the upgraded form of Zero's original body. Model O can't be obtained in Easy mode.

Model O is not a significant part of the storyline (Flammole however states, that he didn't sense the Model W Core or the player, but something entirely different, which might be Model O). Also, official art for OX Vent and OX Aile seems to portray them with sinister gestures (Vent appears to be laughing wildly or screaming in a berserker state, slightly similar to Prometheus, while Aile appears to resemble Pandora in her position), probably referencing to Omega's evil personality.

Appearance
Biometal Model O takes on the form an omega-shaped object with brown coloring to indicate aging save for the crystal and eyes which feature a bright blue color. When Double Megamerged, the Model OX user dons armor identical to Omega Zero though there is an additional bit behind the horns.

Power and Abilities
Model OX is one of the most powerful Biometals in Mega Man ZX. Its special moves are the same as those of Model ZX, and by extension, those of Zero in the Mega Man Zero series. It is equipped with the OX-Buster and the OX-Saber (the Saber used by the player is violet-colored, instead of the pink saber used by Omega, and its charged saber attack inflicts more damage than Model ZX's charged saber attack with a larger hit radius), but the main ability of Model OX is its infinite Overdrive, which is used to perform a series of techniques that were used by Omega at the end of Mega Man Zero 3; however, the player cannot perform the 7-hit combo used by Omega Zero. Model OX seems to also possess semi-aquatic abilities as the user's speed remains unaffected when submerged.

OX-Saber Overdrive

 * Arc Blade (アークブレード) - Saber button while in the air. Model OX releases an ice projectile attack, filling the screen with small saber waves in eight directions, combined with a rolling slash.
 * Ryuuenjin (龍炎刃) - ↑ + Saber. A fire-based rising slash from Mega Man X4.
 * Shinkuujin (真空刃) - ↓ + Saber. A thunder-type, crescent-shaped wave of energy from the saber similar to Kougenjin.

OX-Buster Overdrive

 * Charge Shot Rensha (チャージバスター連射) - Standard shots become level-1 charge shots. Also gains double level-2 charge shots (perform the Shinkūjin after this to perform a buster combo).
 * Earth Crush (アースクラッシュ) - ↓ + Buster. An attack used by Zero in Mega Man X2, Mega Man Xtreme, and Mega Man Xtreme 2, that involves punching the ground to spit up four energy charged boulders.
 * Messenkou (滅閃光) - ↓ + Buster with buster partially charged. Zero's Giga Attack from Mega Man X5 in which powerful plasma bolts erupt from a point where the ground is punched, though the color of the projectiles make it look more like the Rakuhouha from X4).
 * Rekkouha (裂光覇) - ↓ + Buster with buster fully charged. Zero's Mega Man X6 Giga Attack, which has mighty bolts of light summoned from the sky and ground.

Trivia

 * If the game is played in easy mode and a cheat code is used to obtain the Model O, when the player falls into a bottomless pit, it will use a colored version of the Model O sprite when the biometal rescues the player, suggesting that the biometal was originally intended to be obtained by fighting Omega in Easy Mode.
 * It is not fully clear if Model O's existence is meant to be canon, or if it is included simply as an Easter Egg. No mention is made of it in Mega Man ZX Advent.