What happens when you break a gigantic magical crystal and then throw it in the sewers? The answer is Rico, the King of the Rats. A rat that got hit with a gigantic power released from the crystal that landed on him. Which gave birth to mutations that gave him immunity to all poisons and diseases, that and control over all the other rats, making him the new rat king. However, with the newly acquired intelligence, he quickly got bored of his servants's idiocy. So what does he do? Tries to steal all the cheese in Equestria, to make a country of rats, with cheese treated as gold? Also showers are illegal.