Known as both the "Embodiment of Evil" and the "Universal Cosmic Destroyer", Giygas is an evil alien who intends to sentence all of reality to the horror of infinite darkness.
With an army of Starmen, Octobots and other deadly war machines, Giygas also uses his immense power to influence certain Earthlings to assist him, such as Pokey Minch and Geldegarde Monotoli.
In EarthBound, most of Giygas's operations take place in the city of Fourside.
Giygas was an alien raised from infancy by a woman named Maria and her husband George, both of whom were abducted from Earth in 1909 (dated as the early 1900s in Earth Bound Zero and Mother 1 + 2). During this time, George studied the alien's PSI powers without their permission, culminating with their escape back to Earth.
Once he matured, Giygas was tasked by his people to ensure that PSI never spread onto Earth. However, Giygas did not want to betray those who raised him, particularly Maria.
In the end, he was forced to detach himself from Maria and begin preparations for the invasion of Earth. Sometime before the invasion, Giygas comes across the Apple of Enlightenment, a fruit that shows the future.
Giygas learns of his inevitable defeat at the hands of Ness, and so he attacks Earth twenty years before this would occur in order to disprove the prophecy.
Eighty years later, the invasion begins, and Giygas is confronted by the great-grandson of Maria and George, Ninten, and his companions.
Giygas's influence is seen across the land as inanimate objects come to life, animals turn vicious and strange aliens begin to inhabit the earth.
During the final battle of the game, Giygas, still hurt by the loss of Maria, offers Ninten to come with him back to his home planet.
Ninten declines this offer, and Giygas continues to attack. Ninten and his friends quickly prove no match for Giygas; they resort to singing a song once shared between Maria and Giygas, and the comforting memories he had suppressed weaken Giygas.
The latter surrenders and retreats, promising that he will return.
Giygas returns to Earth many years later as the primary antagonist of EarthBound, though he vastly differs from his appearance in Mother. In the time between invasions, Giygas, still trying to defy fate, brainwashes Ness's neighbor Porky Minch into becoming his right hand man so that he would be victorious. Giygas gains such tremendous evil power that it destroys his entire being, including his mind, causing him to become undefinable by human standards. As such, Giygas manifests as what can only be described as pure evil; in Porky Minch's words, "he is the Evil Power". Due to the loss of his mind, Giygas becomes irrational and incapable of thought. To rectify this, Porky seals him in the Devil's Machine so that his power would be contained and his mind kept intact. In the final battle, Porky attests that Giygas isn't aware of himself or what he is doing, referring to him as "an all-mighty idiot".
Now wielding a vast cosmic power which he is unable to control, Giygas becomes a threat to the existence of the universe itself. Ten years after the beginning of EarthBound, Giygas initiates the apocalypse. The only known beings who manage to escape destruction are a Starman Junior and an alien insect named Buzz Buzz, who travel back in time ten years. Buzz Buzz warns Ness of the impending catastrophe. Ness is given the Sound Stone and instructed to record the Eight Melodies in order to gain the power of Earth and be strong enough to face Giygas.
In Ness's present-day, Giygas's influence is seen throughout the world, mainly in the form of enemies that Ness encounters. Now existing as the whole of evil power in the universe, Giygas is able to manipulate the evil in the minds of living beings, both human and animal, and can apparently manipulate even the forms of inanimate objects.
In the final battle, Giygas is held within the Devil's Machine, which was created to contain Giygas's tremendous power. During the battle, Pokey shuts the machine off, causing all of Giygas's power to be unleashed; the event surrounds the four children in a chaotic, bizarre dimension of darkness. His attacks are random and incomprehensible, and his speech is erratic and mindless. Although Giygas was too powerful for Ness and his friends to overcome by fighting, he is eventually defeated after Paula calls out to the people of Earth to Pray (including the player), and the combined prayers reach Giygas and exploit his weakness, which turns out to be human emotions (possibly due to his loss of Maria). He fades into nothingness, and his apocalyptic future is erased.
The five phases of the battle are:
Devil's Machine (invincible) and Heavily Armed Pokey (must be defeated to continue)
Wounded Giygas 1
Wounded Giygas 2
- There is major speculation within the Mother community that Giygas was originally intended to return in Mother 3 as an unused boss character after the battle with the Masked Man. Giygas was dropped from Mother 3 due to his fitting destruction at the climax of EarthBound.
- Brainshock is effective against Giygas, although only during a few of his various different stages.
- Giygas is one of the three characters who can use PSI Rockin, along with Ness and Ness's Nightmare.
- Gigyas' first form is a giant eyeball-like window in the Devil's Machine with Ness' face in the center. His second and third forms are undulating red swirls that resemble a screaming face if looked at the right way. In his final form, it is still an undulating red swirl (with the "screaming face" still visible.) His form with the Ness-like face may be Ninten's as he wanted to be his friend.
- It could be possible that Giygas' race had the ability to mix and match different PSI attacks to form 'patchwork' PSI. As these special PSI are made up of different PSI, it is impossible to see what the PSI was supposed to be like. One example is when Giygas used a multiple PSI Freeze attack on Ness' party, even though PSI Freeze is meant to target only one target.
- In Mother 1+2, it is actually possible to defeat Giygas outside of the scripting by poisoning him. Doing so earns no exp and the ending proceeds normally.
- Giygas is also considered by many gamers the most disturbing boss battle in any video game, as his final form resembles a fetus. It is also noted that the overworld before the battle looks like the cervix and the womb. In fact, he is frequently rated number 1 on the Top 10 Most Distrubing Bosses in Non-Horror Games. He is also often noted for being a difficult boss.
- In Mother 3, most people suggest that Giygas's essence has inhabited Lucas's brother Claus at the climax of Mother 3. Another suggestion is that Porky took part of Giygas's being into the future and made him inhabit Claus's body and act as Porky's puppet. (Due to lack of intelligence and weakening his powers due to him controlling Claus's body).
- Giygas' form in Mother looks very similar to Mewtwo from the Pokémon series. It is possible that Mewtwo is based on his design. This theory is backed up by the fact that many of the people who worked on Mother also worked on Pokémon.
- In the original SNES version, after you defeat Giygas, there is a glitch where the Shattered Man is still in the top floor of the museum in Summers. If you let it defeat you, the screen will be black, and nothing can be done. This is because after Giygas is defeated, all the enemies disappear, for some reason not the Shattered Man. This glitch is fixed in the Mother 1+2 remake for the GBA.