Complex sentence: All amusement park operators that present costumed characters enforce strict character performance regulations so that performers are never seen out of character by visitors; in the case of more elaborate costumes, they are never seen "with their head off".
Split into simpler sentences: All amusement park operators that present costumed characters enforce strict character performance regulations so that performers are "never" seen out of character by visitors. In the case of more elaborate costumes, they are never seen "with their head off".