Gameplay
This game contains elements from the Mega Man X series and the Mega Man Zero series. The players are on a 2-dimensional overlay map with sprites where they engage enemies to finish their mission. When a player receives a Biometal, he is able to change form, gaining various abilities, such as the charge moves, or charging the player's weapon with an element of that Biometal; for example, Biometal H will charge the weapon with electricity. While in a special form, using the form-specific abilities use up weapon energy. When the player receives the other half of the Biometal, he is able to perform a different special ability.
Missions are selected from a list, displayed on a computer. The player can freely explore the game world during and between missions, and they must find the specified area themselves. Computer chips can be found to complete the game database. Also, there are Life Ups which fill the health bar. These can be compared to the Heart Tanks from the Mega Man X series. Bosses all have their own individual weak points: it is where the Biometal they're using is stored. Hitting it deals more damage than the other hits, but it also decreases your ranking level at the end of the battle (ranging from one being the worst to four being the best). This also determines the energy level of the Biometal which is awarded afterwards. But even if the level is low, the Biometals can be upgraded with Energy Crystals later. Bosses are eventually resurrected and can be fought again.
Vent and Aile use the M.E.G.A. System (Meta-Encapsulated Granule Awareness System), also known in the original Japanese version as the R.O.C.K. System (Rebirth Of Crystallised Knowledge System), to activate the Biometals (known as Live Metals in the Japanese version) and to transform into a form similar to that which the Biometal was based on. Anyone who uses the M.E.G.A. (or R.O.C.K.) System is called a Mega Man (or Rockman). It is revealed that only survivors of a Maverick raid can harness the Biometals' power and each Biometal has its own type of people it can merge with; compatible people are called biomatches. Mega Men typically hold out a Biometal in front of them and cry out "Megamerge!" to activate the Biometal (In the Japanese version, they shout "R.O.C.K. on!"). This process is called Megamerging
The player initially begins with only Model X, but upon obtaining Model Z, Model X is used to fuse with the other Biometals. This is called Double Megamerge (Double R.O.C.K. On in the Japanese version). At this point, Model X can no longer be used alone for the rest of the game, until after it is unlocked by completing the game with both characters in normal or hard mode. Biometals of the Four Guardians from the Mega Man Zero series are found throughout the game, and these are the only Biometals that can be upgraded with Energy Crystals. These four Biometals use the touch screen in various ways. A seventh Biometal, a special one called Model O, or Model Omega, is available after completing the game and fulfilling certain requirements.
The Overdrive Invoke System (or O.I.S.) can be activated using the Biometals of the Four Guardians, giving special abilities to the player. Model HX, FX, and LX will give the player elemental attributes to some of their attacks (similar to the elemental chips from the Mega Man Zero series), while Model PX gives the player the ability to dash through enemies. By charging a player's weapon, the four Biometals are also able to perform attacks similar to the Four Guardians. For example, Model HX can summon a hurricane and Model PX can throw a large shuriken. However, O.I.S. consumes Weapon Energy or Biometal Energy and is irreplenishable. Model O cannot lose any Weapon Energy because it shouldn't even exist, so it doesn't have a Gauge, because it isn't a Biometal and doesn't make use of the M.E.G.A. System. It does make use of the Bio Energy Sync Mergers System, or B.E.S.M. System to merge with Biometals before the Megamerge, though.
Players can also revert to Humanoid form at any time. Although Vent/Aile cannot attack, dash, or wall-climb without a Biometal, they are able to swim and crawl. They will float on the surface of water instead of sinking. Some N.P.C.-s are too afraid to speak to Vent/Aile when they are using a Biometal, and security bots of the city will not attack unless megamerged with a Biometal or outside Innerpeace.
Read more about this topic: Mega Man ZX