Giygas is an evil alien force unleashed by Pokey Minch to wreak havoc on the earth in EARTHBOUND. In SuperSpy Luigi, he was a temporary main antagonist until Luigi defeated him. He has no actual form, so he is never seen for real.
Giygas is shown to be a homocidal maniac with insane bloodlust. He as PTSD (Post-Traumatic Stress Disorder) and has terrifying flashbacks because of it. Giygas takes out his anger on others. If anyone mentions rape near him, he goes wildly out of control.
"Come Bill, we can rule the galaxy...forever...you musn't resist..."
"Why do you hate me.....I thought we could be friends...."
"I'LL SQUISH YOU LIKE THE PARASITE YOU ARE!!! DO...DON'T.....RE.....RESIST!!!!"
"It hurts, Ness...."
"IT'S NOT RIGHT...N-NOT RIGHT...."
- Giygas was created from a traumatic memory of his creator. The Creator went into the wrong theater and saw a rape scene in a movie. He thought it was real. He even told the police what happened. Giygas represents the "pain" the woman in the movie went through and the Creator's emotions.