Adestefidelis is a forbidden spell which causes "Jingle Bells" to play continuously in the victim's head. Death by this spell comes quickly, usually by the victim's own hand to end the psychic torture, though it is implied that the spell will finish the job. The spell takes the form of a red-and-green bolt of light and must be aimed at the forehead. The incantation is the name of a hymn, Adeste Fidelis.
Barry used this spell on Dirty Dimsley just after Dirty had been attacked by a focus group.