Spirits of the deep that never sleep.
Spirits of the grave without a soul to save.
Spirits of earth and fire, destructive in their ire.
Spirits far and near, feasting on our fear.
Devils, demons, ghouls, and ghosts, elect of all the devilish host, we pray you bring hither, bring hither, bring hither, the great grey shape that makes men shiver.
Pray heed our rhyme, we'll serve you for all time.
Taken, in part, from a real werewolf spell from the Middle Ages. It's safely out of copyright, and I doubt the Devil would complain about spreading this one a little wider anyway...