Giga Metal[note 1] is a transformation that appears in the Sonic the Hedgehog series. It is the result of Metal Sonic combining his power with that of the Phantom Ruby's, resulting in a gargantuan robot with many unique abilities. Dr. Eggman utilized to his advantage in order to defeat Sonic and his friends in Stardust Speedway Zone.
Much of Giga Metal's design borrows heavily from its base form, though Metal Sonic now stands many feet taller than his original form. By comparison, Metal Sonic is now more bulky, with a larger torso and a smaller head. His metallic quills on the other hand have grown longer and now extend down his spine. His ears and nose have also grown longer, while his eyes have become a lot narrower, being little more than a red line. He also now has yellow bolts on his cheeks and a yellow cannon below his chin. His shoulder plates have become larger and longer as well, with their coloration having changed from gray to blue. They also have several cables attached to them that extend underneath them. Lastly, he has a glass covering the intake on his stomach, which contains the Phantom Ruby.
In Sonic Mania, during the final phase of his battle with Sonic, Tails and Knuckles, Metal Sonic received the Phantom Ruby from Dr. Eggman. The ruby's power allowed Metal Sonic to transform into Giga Metal, and he proceeded to fight the heroes with renewed power. However, by shattering the container on his chest that held the Phantom Ruby, the heroes managed to shatter the illusion that created Giga Metal's form, resulting in Metal Sonic's defeat.
In his Giga Metal state, Metal Sonic possesses much greater physical strength, enough to walk through metal roads like they were made of paper. He also gains a cannon that can fire lethal energy beams and deploy timed bombs.
As Giga Metal, Metal Sonic loses much of his original form's speed, although he is still able to keep up with the likes of Sonic. The container on his chest that hold the Phantom Ruby is also a weak point, as shattering it will undo Giga Metal's transformation.
Giga Metal appears during the final phase of the boss battle with Metal Sonic in Stardust Speedway Zone Act 2. During the battle, Giga Metal will constantly approach the player from the left while either firing a laser beam or dropping timed bombs. In order to defeat him, the player has to strike the container on his chest a total of eight times.