A good example of Loki's evil mind is when he tricked Hoedur the Blind into shooting his brother Baldur with an arrow made of mistletoe. He got severly punished for that and now he's kept in chains, deep down in the earth. A snake hangs over his head and the snake's poison is supposed to drip continually onto his face. His wife, Sigyn, however, sits by Loki and holds a bowl over his face, into which the poison drips. Every time she gets out to empty the bowl, the poison drips into Loki's face. Then he gets cramps so fierce that the whole earth quakes. We call that earthquakes.
Some say that Loki made the worst creatures in the world because he is the father of the monsters Hel, Fenrisulfur and Midgardsormur. The giantess Angurboda is their mother. Those monsters wil play an important role of evil when the world comes to an end.