The way Mommy Long Legs says "A new playmate! It's been so long..." definitely sounds more sadistic than friendly. She most likely enjoys toying with her food, much like how many arachnids like to watch their prey struggle in their web until they finally either exhaust themselves or simply give up. Considering the spider theme and the title of the new chapter, I think this could be the most viable explanation.

Maybe what Poppy is referring to when she says "Mommy doesn't like guests" is that being a guest means that you eventually have to leave and Mommy wants to make you a resident and never let you leave? Mommy doesn't like people who leave her

I just think it’s meant to reflect her ‘spider’ like nature, sly and sneaky: pretending to be nice and kind but waiting for the right moment to pounce. Poppy of course warns us before this: and I can imagine a bit later on she would switch completely into a different voice, trying to kill us instead of pretending…just how huggy was pretending to be lifeless and just normal.

Another thing to add to the theory: In the scene of Huggy being dragged away, the hand that does it is almost the size of Huggy himself, but in the scene that shows what is believed to be Mommy Long Legs, she seems to be about Huggy’s height according to the perspective.

Something I noticed is that if you (RESPECTFULLY) look at her chest, you see the top of a sweetheart neckline of her dress. That look is very common when it comes to old fashioned mothers in cartoons. The sweet heart neckline is often meant to accentuate the bosom and is considered a very mature look. So while I Very much like the idea of the first theory, I definitely think it is closer to the last theory. But I also thought about how growing up, I liked to play house. So when she says "a new playmate," she might even be thinking of someone new to play house with. With a name like "mommy long legs" it is very easy to associate this character with a motherly personality in turn. But since all of her old playmates most likely been destroyed, she has probably been craving to feed that motherly instinct that she was built to have.
Okay I have said my piece! Great video! And I had not heard about the ARG! I will definitely be looking at more of your videos for more poppy playtime lore and theories!

I feel like Poppy’s line meant to convey that Mommy Long Legs is extremely dangerous and kills people who wander and maybe not that she literally hates guests

But your child theory also makes a lot of sense

Listen to the way she says "It's been so long", her voice is menacing, she definitely plans to do something to the player. Honestly, I don't think the pink thing is necessarily a child; if you take in consideration that the souls of the missing staff are probably trapped inside some of the toys, it might make more sense to think that whoever was tied to the pink thing had their soul warped to be something childish but also evil, just like it might've happened to Huggy Wuggy.

I always thought it was strange calling her Mommy Long Legs, when she seems to be a newer toy, or at least younger than Poppy. Might be bc she's based on Betty Spagetti, but she gives me more of a crazy teen girl vibe.

My theory is that she says "A New Playmate!? It's been so long..." She is referring to you as a meal she could play with before devouring, and the games second chapter is literally called "Fly in a Web." As Poppy infers: Mommy Doesn't Like Guest, this could be the exact reason she came towards you, to just get the whole thing over with and, well... *Game Over Screen Plays*. I also think that maybe her other 4 legs are hidden behind her, but thatch just my guess though.

7:49 Omg! I remember Betty Spaghetti. Used to have a doll as a kid. Mommy Longlegs looks so much like her.

I think she’s just happy to see another “human” to kill them and play with their food like spiders do

Same I though that mommy long legs the way she was introduced to us was a little bit strange good work by the way

She doesn’t like “guests;” she likes “food.”

That’s what they went for. 100%

ALSO! If you count the “hair,” she has 8 noodles.

Pov: watching this after the chapter comes out

I had Betty Spaghetty as a kid and it's beyond similar. Mommy Long Legs has the same arms with the little holes that Betty had. The same oversized hands, the ponytail in the same spot, the same little painted lips. It's spot on.

I think it's more likely that it's someone else that's so aggressive, but if poppy WAS referring to mommy long legs "not liking guests" (being the pink squiggly toy) it could be referring to the juxtaposition of her desire to play and have companionship and HOW she likes to play. She may like guests, but not LIKE them as a normal person would, having much more sinister intentions. And since poppy seems fairly genuine it could fit. I LOVE the Betty spaghetti idea. Seeing them side by side, I think it's a direct reference, but not sure how far that goes.

Mommy Long Legs could also potentially be defeated with a tear-apart like method. We saw Huggy Wuggy fall from great heights, while losing some blood. I imagine she may face a similarly dark demise, since MOB Games clearly isn't afraid to add some gore. While the theory that the pink spider character is a child theory is a good one, she may just as easily be a grown up, but with a very cutesy appearance. As others have stated, her friendly-childlike approach could be one that's intended to give the player a false sense of security. She may just be seeking her next meal or kill, either for herself or her children. It would make sense that she wants someone to play with her kids, since that's something all mothers figures look for.

Edit: to add on to your theory that her appearance may see changes later in Chapter 2's plot, like Huggy Wuggy, I think her eyes might become more creepy, or she could attach extra legs. Maybe her eyes will become fully black? That'd be pretty horrifying!

I fully agree with both theories in that she has another form or is the daughter of the real mummy longlegs, though I'm leaning more towards the latter due to the quote "Mummy doesn't like guests."
It could also be, adding onto your theories, that she is an "older sister" of a lot of toys and wants to keep them safe or use them in some nefarious way.
A playmate for her? Or a playmate for her siblings?

Im curious about Poppy refering to the player as "Perfect" and "too perfect to let go".  It could still be a reference to the fact the player isnt a real human but a very accurate and "perfect" doll made to look and act human.

It's interesting to watch old theory when the actual game came out to see the what the community has speculated