Meet Porky Minch. In Earthbound, he's at best kind of a jerk, and at worst a real jerk who's playing even Giygas for his own desire for power and incredibly petty desire to mess with Ness. Come Mother 3, though, his evilness is turned right past eleven and up to fifteen, as he turns a rather simple, peaceful island into a needlessly materialistic society (his view of utopia), tears apart lead character Lucas' family, and then proceeds to enlist the help of the Masked Man (A.K.A. Lucas' twin brother Claus, almost killed by one of Porky's own creations and brainwashed to serve Porky) to summon the Dragon (not that one) to completely destroy the world. Even reading all of this doesn't convey the message of how truly sickening this guy is.
And his reasoning for killing all these innocents, corrupting the island's nature, and almost destroying all of existence is...he was bored.
It's worth noting, however, that there's very subtle implications that Porky's true, original motive, the beginning of it all...may have been an inferiority complex. In Mother 3, Porky keeps memorabilia of Ness and his party on display, and in the Japanese version of Earthbound/Mother 2, it's implied that he may have been abused by his father. Could it be possible that Porky envied Ness, being weak and helpless in comparison to him, but due to his selfish nature and Gigyas' influence, he lost himself to depravity? There's no way to know now.
Perhaps the most telling implication is his theme song, entitled Unfounded Revenge. In Earthbound, he is first met trying to get past a police barricade, to the apparent annoyance of the policemen, and Ness is asked to take him home. Throughout the game, it is obvious that most of the characters think he's an annoying pest, right down to his own parents. Thus, it is implied that he wants revenge against EVERYBODY THAT EVER EXISTED for ignoring him. This is further shown by the fact that he keeps the "Friend's Yo-yo" as his most prized possession, a memento from Ness, Ness being the only one to pay any attention to him and the closest thing he had to a friend.
Porky is one of the most confusing villains ever. He's essentially a 12-year-old kid in a 10,000 year old body who got picked on by everyone back at home. In spite of literally being the king of the world, he wants to destroy everything because he thinks no one likes him. He can no longer die and he's sick of everyone, so his motivation for destroying the planet is so he can be the only one left in it (a wish he eventually gets, in a twisted way). But in the end, you can also see that he's essentially a little kid who was robbed of his childhood, and the two things he misses most are his neglectful and abusive parents and Ness, a boy he made a sport out of screwing with. I should mention that everything he did to Ness, he essentially thought was the same as "playing a game with him". The reason I say he's a confusing character, really, is that while I can't think of him as anything less than a complete monster, there's still sympathetic elements to him...he's absolutely horrible, but you can understand why he has become a monster.
For anyone who has watched an episode of South Park, Porky becomes a much less confusing Complete Monster. Just imagine him speaking with Cartman's voice.
