Complex sentence: The guests see bizarre presents instead of hitchhicking ghosts when they go by the mirrors and if the present is a coffin imprinted with a question mark, Lock, Shock, and Barrel will pop out from behind each of the three mirrors.
Split into simpler sentences: The guests see bizarre presents instead of hitchhicking ghosts when they go by the mirrors. If said present is a coffin imprinted with a question mark, Lock, Shock, and Barrel will pop out from behind each of the three mirrors.