Mary was a Replicant that was written out of the script at an early stage. She was to be a mother-figure, Nanny-type Replicant, performing housework and childcare duties. She was one of The Six Renegade Replicants led by Roy Batty. She, like Hodge was one of The Six Renegady, was written out of the script at an early stage. She would have been present for the outer colony escape, but the sequence was scrapped in favour of an opening crawl.
In the Final Cut it was mentioned that she was killed when she was fried by passing through a security measure called an electro-field while breaking into the Tyrell Corporation headquarters. 
When Mary was excised from the script, this created a small problem: Bryant should be saying that there are three remaining Replicants (Roy Batty, Pris and Rachael), not four. Rather than re-shoot this scene, they rearranged the scenes during editing and put Deckard's confrontation with Leon after he bought his Tsing Tao, so that the four remaining Replicants would be Roy, Pris, Leon (not Mary), and Rachael. However, this created its own errors:
- In previous cuts of the film, when Deckard is buying his Tsing Tao and later talking to Bryant, he has a scrape on his face from his fight with Leon before it's even happened. (Fixed in The Final Cut.)
- Since he now buys his bottle before he fights Leon, it should be there while he's fighting Leon (it's not). The bottle mysteriously reappears when he gets back to his apartment. Considered a "beloved flaw" by Scott.
Mary was to be portrayed in the film by Stacey Nelkin, who originally auditioned as Pris.