The implications of “Yenndo” makes the Bite a 100x worse
Don’t get me wrong; the Bite shown in 4 is already pretty bad as it is. However, apparently that wasn’t enough for Scott, because Yenndo manages to kick it up another ten notches.
Let’s start off with the basics for those who aren’t up-to-date on theories. First, we know “Yenndo“ is exactly the same as Funtime Freddy’s endo, except it has yellow eyes (and two hands). Secondly, its behavior in the Custom Night parallels Golden Freddy’s in FNAF 1. Between these two things, we can safely determine that this is actually an endoskeleton of a Funtime Fredbear - something that’s only supported by its nickname (Yenndo = Yellow Endo).
However, we know that Funtime Fredbear isn’t the same Fredbear shown in 4. FT Fredbear is shown to have multiple plates, while FNAF 4 Fredbear is covered in solid cloth. Likewise, FNAF World implies FNAF 4 Fredbear has teal eyes, not the yellow eyes of FT Fredbear, and the map in SL indicates it should have been on stage around the time of CBEAR. Instead, it’s much more likely that it originates from the original Circus Baby’s Pizza World.
(It's also possible that, while the endo originates from CBPW, it was stripped of its suit plating and refurbished into the Fredbear seen in FNAF 4. This is why it's a bear bare endo - they haven't put it into the new suit yet (though this only works if SL takes place very shortly after CBPW opened).)
Now for the bigger question: Why does it exist, and what impact does it have on the story? To answer this, we just need to look at the blueprints for Funtime Freddy, who shares more or less the same endo. And, as you can see, one of FT Freddy/Fredbear’s main features… is a “storage tank“ located in the torso.
Now, let’s pretend you’re a small child visiting CBPW. You leave the room momentarily to get a snack. You come back, peek around the corner… and witness what appears to be a small child getting “eaten” by a “mouth” on Fredbear’s stomach.
But hey, it’s not like there’s anything in FNAF 4 that portrays Fredbear with a mouth on his stomach, now are there?
(Credits to Springtrapattacks here for this connection.)
The implications of Nightmare Fredbear and FT Fredbear are simple: The Bitten Child witnessed another child getting killed by FT Fredbear, and then projected that fear onto FNAF 4 Fredbear, unable to tell the difference between the two of them.
Which leads us back to the Bite: Where the Brother, unaware of this fact, picks up the Bitten Child,** brings him to the animatronic the Bitten Child (thinks he) witnessed murder a kid by “eating” them - and sticks his head in the thing’s mouth **. If the Bite wasn’t bad enough before, it’s far worse now that we have a child being forced into a situation that he basically has PTSD over.
TL;DR: “Yenndo“ is a Funtime Fredbear, and the Bitten Child witnessed it crush a kid in its torso compartment. The Brother bringing him up to another Fredbear and shoving him in its mouth would have only terrified him more thanks to this memory.
