Amie Donald, a 12-year-old national champion dancer and brown belt in karate who was discovered "at a farm down the road," provided the full body moving shots, including all the stunts, and the dancing scenes for M3GAN. Director Gerard Johnstone said in an interview: "The methodology was essentially to use an animatronic puppet when she's still, and as soon as she starts moving she's a girl in a mask," and that it had only been possible because the "incredible young actress" had physical abilities he hadn't believed anyone would have, and was so completely dedicated she would work out how to do anything he asked of her. Donald received coaching from Luke Hawker, a movement coach used to working in prosthetics, and worked with a stunt team (who she amazed by not needing any wires or rigging to perform the superhuman feats). On set, Donald wore a static silicone M3GAN mask created by Morot FX, which was later animated with CGI for M3GAN to appear to be speaking.
The film was originally R-rated by the MPAA. While editing, it was evident that it could be a PG-13 rating by altering a few scenes, and attract a larger audience. Due to the trailer's popularity among teens, some scenes were reshot to tone down the violence and obtain a PG-13 rating.
Adrien Morot and Kathy Tse of Morot FX Studio created an animatronic puppet version of M3GAN that was used for dialogue and close-ups. There was also a second animatronic used for certain scenes, as well as a posable stunt version of M3GAN that wasn't puppeteered. The animatronic M3GAN was puppeteered via a variety of techniques, which included radio-controlled facial expressions performed by Adrien and Kathy in tandem, automated lip-sync for the dialogue (temp tracks were provided during filming by New Zealand actress Kimberley Crossman) and a puppeteer physically moving M3GAN's head and body.
The idea for the film began when James Wan's Atomic Monster Productions was brainstorming story ideas and chose one about a killer doll. Although the Wan produced film Annabelle (2014) is about a killer doll, he said, "Pretty much the concept is about embracing technology too much and relying too much on it. And what happens when technology runs amok. It's a commentary on the world we live in and it feels relevant." Jason Blum stated that the film would have black comedy elements which is one reason Gerard Johnstone was chosen to direct, saying "We needed someone who can do the thrills and set pieces, but who also has a cheeky approach." Wan admired Johnstone's film Housebound (2014) because of his ability to balance the horror and comedy elements by creating a tone that is both frightening and humorous, and this sensibility was essential for M3GAN.
