The Beasts are a group of Goth boys at Franklin Grove who're vampires like Ivy and her friends. The group consists of Garrick Stephens, the leader, and his three best friends Ricky Slitherman, Kyle Glass and Dylan Soyle. Even though they try to project a tough guy/bad boy-image, they're serious wimps.
Their names weren't revealed until the second book, when they almost reveal the existence of vampires. In Fangtastic!, it's revealed that ever since they and Ivy were little kids, the Beasts have always been pulling really stupid stunts, such as seeing which of them could eat the most garlic croutons without getting seriously ill, and have come routinely close to breaking the First Law of the Night: vampires are never supposed to reveal their true self to an outsider.