Amie Donald performed any of M3GAN's scenes that called for physical movement the puppet could not do. She also performed all of her own stunt work. Donald received movement coaching from Jed Brophy and Luke Hawker in portraying M3GAN's agility. On set, Donald wore a static silicone M3GAN mask created by Morot FX, and this was later replaced by a CGI version of M3GAN's face to match that of the animatronic.
The film was originally shot as an R-rated (by the MPAA - other countries use different classification systems) movie until the producers noticed while editing that it was close enough to PG-13. They re-shot certain scenes to tone down the violence and believe that it became more effective than actually seeing the violence on screen. Jason Blum cited Drag Me to Hell (2009) as a good MPAA PG-13 horror film that was effective.
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.
M3GAN's voice is modelled, in part, from another famous artificial intelligence-gone-rogue, GLaDOS, from Portal (2007). This is most noticeable during scenes when M3GAN's voice is auto-tuned in order to sound 'glitchy'.