The Brotherhood III: Young Demons (2003)

A group of devil-may-care teenagers discover they've mistakenly called upon the Prince of Darkness in this flashy horror story. A handful of high school students have been entertaining themselves on weekends by playing an elaborate role-playing game in which they impersonate witches, warlocks, and other magical beings. One weekend, they decide to up the ante by breaking into the school and using the building's nooks and crannies to make the competition more challenging. One of the teens has brought along a book of magic spells, and they decide to throw some incantations into the games to make things more interesting. What the kids didn't count on is that the spells actually work, and soon the role-players have unleashed an unspeakable and dangerous force.