fucked up has collaborated extensively with other artists on record and during live performances. hidden world features guest instrumentation from final fantasy, and guest vocals by ben cook of no warning (2 years before he joined the band), george pettit and dallas green, formerly of alexisonfire, chris colohan of cursed, and heidi hazelton. year of the pig was written in part with max mccabe-locos of the deadly snakes, who plays piano and organ on the record, and a lead vocal by jennifer castle of castlemusic. in late 2007, the holiday charity single david christmas featured guest vocals from nelly furtado, davey havok, david cross, shenae grimes of and faris badwan of the horrors, among others.