So my theory is that the neighbor in secret neighbour is the shadow man or what ever that guys name is. Need proof well that's why I'm here

Evidence:

let's analyse the neighbor first normal he is pretty clean and although crazy it doesn't show in his face. However, in secret neighbor he is dirty and notably more insane than usual. Now secret neighbor our is said to take place just after nick gets taken into the basement hence the aim of the game is to save him aswel as the fence walls surrounding the house wich is un act 2 of the full game. And this means that the shadow man is still haunting mr peterson and Mr.peterson is probably down in the basement working on stuff like defences and keeping nicky below the house, witch could also explain why he is dirty [and also his hair flick is flattened in this game too] but the biggest things that scream "I am shadow boi" is the hole "secret neighbor" part of it. Now I know this is a spin-off but tiny build confirmed it is all cannon and too did the vr game AND cartoon. So when the neighbor begins he is OUTSIDE the house with the kids and DISGUISED as one of them. When the neighbor transforms we can see black particles surrounding him ad a black dark matter swirls and boom the neighbor, but if we look at those particles and dark matter the particles are the same shape and size [maybe a bit smaller] as the ones surrounding the shadow man. And also we never see the neighbor shape shift at all and there doesn't seem to be any technology in the mix of it.

Final notes:

The shadow man also has his own Easter egg were when the neighbors health has dropped fully he dissappear and the shadow man appears [slightly thiner and different shape but its confirmed as the thing Easter egg]

So there you have it I am fully convinced that I know your secret neighbor!

Any other thoughts anything I missed or any arguments to that let me know

Alright I can conclude that the neighbor in secret neighbor is the shadow man thing whatever

BUT HEY THATS JUST A THEORY A GAME THEORY THANKS FOR READING [piece to my man matpat]