Giygas

From Mother - Wiki on Neoseeker

WARNING: Contains Spoilers That May Ruin Your Gameplay

Overview

Giygas is a being of pure evil. His power is so immense that he is a danger to not only the universe but to himself. After gaining an incredible wealth of power, he destroyed his own mind and became insane. This power did not go to waste-even in the Devil's Machine Giygas managed to influence the animals and creatures around the world to slowly destroy the world and take it over from the inside out. His true origin is unknown but it is theorized and most likely is true that Giygas is the spirit form of Giegue from Mother 1 after becoming so powerful that he destroys his own body.

Giygas was defeated by the prayers of Ness and Co.'s Family and Friends via Paula's pleas, including the Player him/herself!

Giygas was originally supposed to appear in Mother 3, but didn't due to Itoi wanting to make the ending less dark and not betray the player. He was originally supposed to be in the body of the Masked Man, and Porky would be controlling him until he was defeated, then he would escape and battle you.