“ Now there's just one more thing left... the story of the Evil Pigs. ”
—10,000 Year Old Man
Source of Evil Magic (魔力のみなもと？, Maryoku no Minamoto, lit. Origin of Magic Power) is an event in Tomba!.
Find the Million Year Old Man and let him tell the story about the Evil Pigs and its origins.
Note that the Unbreakable Wire event must be cleared in order to get access to him. When it's done, head over to the Million Year Old Man's hut and enter. The event will be cleared after the conversation.