Hiya! I just watched a video (linked in Notes and Credits) and I have a quick theory I wanted to share! So Sheeprampage on YouTube just did a theory video about how the writer of this letter (shown in the project) could be Marcus Brickley, a Playtime Co. employee played by Jackspticeye on YouTube. Watch the video first, then read this. Did you watch it? Okay good, cause he's much better at explaining than I am. So my theory; Mommy Long Legs, or at least the woman who was Mommy Long Legs in Chapter 2 of Poppy Playtime, is the mother of Marcus Brickley. Here's my explanation: So Marcus was interviewed on March 21st, 1991. In July, he sent the letter; the same year Mommy Long Legs was created. My theory is that his mother did investigate the company of Playtime Co. after her son's disappearance but was caught by the company and they decided to "take care" of her. This being, she was experimented on and turned into Mommy Long Legs. I'm guessing that Mommy Long Legs the toy was either created specifically for Marcus' mother or was already planned and needed a person to test her with. This would also explain why she's so loving and protective of the other experiments as stated in a letter from Chapter Two; she's a mother herself, and she misses her son and doesn't want anybody to be hurt. (Update to this theory about 20 minutes after making this: yes, Marie Payne was the original name of Mommy Long Legs before becoming an experiment, but I think I have a theory as to why that's the name. Possibly, Marie Payne could've been Marcus' stepmother, or she was widowed and got married to a man with the last name of Payne once Marcus was an adult.) Anyways, that's my theory, sorry it was so short! It was something I randomly thought of and needed to express in words.
References from this video https://youtu.be/vwbROlNspY8 Photo from a letter sent to content creators by the creators of Poppy Playtime