It was used by John "Jigsaw" Kramer, often appearing on a television screen, or occasionally in person, to describe the details of the traps and the means by which the test subjects could survive.
However, Jill Tuck, his wife, is shown to miscarry after being hit in the stomach by a swinging hospital door due to Cecil ramming it open without looking.
Billy is a male ventriloquist's dummy, as its jaw is movable to give the suggestion that it is talking; however, it is not used in the same manner, as the entire doll is frequently seen moving on its own.
According to Wan, the construction of the original puppet's face for Saw involved clay, papier-mâché, and black ping pong balls with the irises painted in for the eyes.
Instead, they recreated Billy, using waterjet-cut foam for his body instead of fiberglass, equipped with plates to hold the puppet together and magnets to attach him to his tricycle.
In the first Saw film, Billy is seen on a television set by Amanda Young, telling her about the reverse bear trap that was hooked into her jaws, and explaining that the key to remove it is in the stomach of her "dead cellmate" (who is actually a heavily sedated man) lying in the room.
As he searches the dark rooms using his camera's flash, the puppet's eerie laugh rings through the apartment, and Adam hits it with a bat until it stops.
When Detectives David Tapp and Steven Sing discover Jigsaw's latest hideout, they remove blankets from several covered items, one of which is Billy.
Later, when the detectives discover Jigsaw's new hideout, several officers walk up a caged staircase and are greeted by Billy, who wheels into sight at the top of the stairs on his tricycle and laughs.
Upon leaving the room, Rigg is greeted by another message concerning his first test, referring to a woman Jigsaw deemed to be a criminal, who had been placed in a machine that would scalp her.
Agents Peter Strahm and Lindsey Perez later find Billy in a room in a school, sitting on a chair surrounded by candles.
From a microcassette recorder hung around the puppet's neck, Perez learns that her partner will soon take the life of an innocent man (later revealed to be Jeff Denlon), and that her next move is critical.
There is also a flashback of Jigsaw giving a less menacing, early version of Billy to Jill Tuck as a gift for their unborn son Gideon.
Masquerading as police detective "William Schenk", Emmerson showcases his own new puppet "Mr. Snuggles", inspired by both Billy and the pig motif of the previous films.
After Valentina failed her test, Amanda tases Mateo and restrains him on a wheelchair, putting an open mask around his head and an electrical circuit around his torso.
After Mateo fails his test, Billy appears next to Gabriela with a similarly marked "Play Me" tape around his neck ready for her game to commence.
Billy the Puppet is featured on some cosmetic items, such as a car decal, in the popular free-to-play online game Rocket League from 19 October 2022 as part of the Halloween update titled "Haunted Hallows".
A costume of Billy was added to Call of Duty: Modern Warfare for Warzone operator Morte as a part of The Haunting of Verdansk event.
He can also be seen before the car travels up the lift hill, appearing on a screen and saying "Game over", and at the end of the ride, where his head can be seen on a shelf covered with body parts.