As befitting the avatar of an entity of destruction, Rahu is the most powerful robo in Custom Robo (GameCube). Each of its forms are unlocked in the second story campaign, "The Grand Battle".
It has three forms: Rahu I, Rahu II, and Rahu III, with its final form having the highest stats of any robo in the game. Its body, gun, and pod change as it evolves, but the bomb and leg remain the same.
This is Rahu's basic form. Its form is distinct from any other robo, having a somewhat incomplete, skeletal appearance. Its base structure consists of masses of red and blue wires woven through whitish-grey metal limbs, resembling organic bone and muscle structures. Two large, horn-like structures protrude from the back of its head, and it has no visible facial features apart from a red visor. When using its extended dash, it appears to make running motions as opposed to compressing itself into a jet-like form.
Rahu I is effectively a Lightning Sky model, but with higher overall stats. As such, it works best when played as you would any Lightning Sky robo; weapons that benefit from being spread around the arena or used in hit-and-run tactics. The Eagle and Afterburner guns work well with Rahu I, but its namesake gun (Rahu I) is also quite effective, being an upgraded Flare with bigger blasts, higher rate of fire, and more damage. The Penumbra I pods fire ground-hugging homing projectiles similar to the Seeker, but with more speed and damage. Its Grand Cross bomb creates four explosions in each of the cardinal directions relative to Rahu's position, while the Ultimate legs increase all of its movement attributes.
Rahu II is the form taken by the enigmatic being during its modifications in the Z Headquarters. It appears similar to Rahu I, but with light grey armor added to various parts of its body, making those parts bulkier. The armor placement is haphazard and heavily asymmetrical, indicating that the upgrade is not yet complete. Rahu II is basically a more effective version of Rahu I, having a similar stat layout but higher stats. Thus, it can be used in basically the same manner as its weaker counterpart. Its gun and pod have been upgraded as well, but the main differences are increased range, damage, and area of effect.
Rahu III is the third and final "form" taken on by Rahu over the course of the game. The armor developing on Rahu II has grown to cover almost all of its body, making it look more "complete". Its head has changed dramatically, losing the horns and taking on a dragon-like configuration, with many small spikes erupting from the back. However, a red marking near the "snout" may indicate that the visor is still in place, giving Rahu III a truly unique head design. The robo's overall bulk has greatly increased in this form, making it appear similar to a Metal Grappler model.
Rahu III plays somewhat differently than its earlier forms. It isn't as mobile as its other two forms, and its charge is slower and less ranged than Rahu II's brutal ramming attack. However, the charge allows Rahu to get higher in the air than if it did a jump. Rahu III is also outfitted with a second long-range air-dash, which allows it to more than make up for its lack of ground speed. Its eponymous gun, Rahu III, emits enormous rounds after it explodes, usually enough to cover all stages except Gigantix Sprawl, and deals crippling damage if a point-blank hit is delivered. The Penumbra III pods are the fastest of the three, emit blasts similar to those of the Grand Cross bomb, and can be launched three at a time. More impressive still, Rahu III is effectively immune to knockdowns; any attempts will simply cause it to enter Rebirth without any down time (although it does dissipate any shots it may have fired). All of these traits make Rahu III the most powerful robo in the entire game.