If you think there's just one fake sideshow on the list, I have some magic beans to sell you. Sideshows have historically been rife with hoaxes, and in some ways they're even more fun than the "real" acts — there's something of a relief in seeing the audience exploited as opposed to the performers. Pasquale Pinon — also known as "The Two-Headed Mexican" — is a kind of in-between sideshow performer. Although (spoiler!) he didn't really have two heads, he did have a medical condition that gave him his start.
Pinon was actually a rail worker in Texas with a large tumor growing from his head. A promoter saw him one day and like any reasonable person, thought, "Ah, I should absolutely pretend that's a second head and put him in a travelling show." They put a wax mask on the tumor so it resembled a (frankly super-fake-looking) face, and basically had Pinon sit quietly as strangers gawked [source: Pednaud].