The Custom robo is the centerpiece of the Custom Robo world. They are miniature robots that have effectively become the new standard of conventional weapons. The average Robo is 8 or 10 inches tall, but nonetheless very capable of immense destructive power. While robos are usually deployed inside the virtual environment of Holosseums, some robo commanders have government permission to deploy their robos in the real world to stop renegades. When not in use, robos are stored as compact cubes, in both the virtual and real world. Sometime before the events of Custom Robo (GameCube), Robos were restricted to functioning only within the holosseums, incapable of existing in the real world except in inactive cube form.
There are many varieties of Robos, each which possess different skills. Every Robo must be equipped with a Gun, Bomb launcher, Pods, and a pair of Legs, all of which function in different ways. Guns are a robo's right-handed weapon, and primary means of attack. Bomb launchers are carried with the left hand, and produce a variety of explosive effects and trajectories. Pods are AI-controlled explosive drones, mounted on and launched from a Robo's back. Legs provide modifications to a Robo's overall movement abilities, whether it be enabling the robo to run faster, augmenting their jump height or air-dash speed, and so on. Every robo also possesses a Charge attack, which (in most cases) sends the robo charging forward to ram into an opponent.
Competitive robo battling involves two (or more) Commanders competing either as teams or all against each other. A match starts with a Robo Cannon firing the inactive Robo Cubes onto the Holosseum. When the cubes settle, the robos begin to activate, slowly transforming out of their cube form and into their fully-functional combat mode. A robo that begins to transform on its side, back, or front will be able to become battle-ready in a short amount of time. A Robo that begins to transform upside-down on its head will have to right itself after transforming, making the time it takes to start fighting longer. A robo that begins transforming on its feet will have the shortest amount of helplessness. In Battle Revolution, however, the manual transformation process has been replaced with a countdown, each Cube being assigned a random starting number from 1-6, with the Robo fully transforming when the countdown hits 0.
In the battle proper, robos start out with 1000 Hit Points each. As robos incur damage, their HP drops in value accordingly. Once a robo's HP hits 0, it is knocked out, and removed from competition. The winning commander or team is the one with the last robo(s) still active. If a robo suffers significant damage in a short amount of time, or is hit with special high-impact attacks, it will overload and fall down; otherwise known as a Knockdown. When knocked down, a robo must struggle to restart itself and get back up, during which time it can still suffer damage but at a reduced rate. When restarted, a Robo enters Rebirth, where it becomes temporarily invincible. Some Illegal Robos, while not outright immune to knockdowns, will immediately enter Rebirth with no vulnerability period.
When combat occurs in the real world, robos start out in their full combat forms, without the use of the Robo Cannon.