Fancy Man of Cornwood
A one way mirror. The characters can't see through it, but we can. Characters breaking the fourth wall realize that they're being watched when they peer through a small crack in it.
Hello? Hello, hello?
I assume it's some sort of transparent glass. 
A square window with a portal aura around it.
"Listen up, Marina, because this is SUPER important. Whatever you do, don't eat th“ “DON'T EAT WHAT?! Your text box ran out of space!”
Extreme math nerd
The Blender viewport camera model
? Alternatively, a fully transparent rectangle with a high refractive index, which turns into a picture of a viewer when focused on.
A PICKTURE!!!
an tv screen, obfuscated by an wall with a painting of wherever the characters are in. the painting wall is what they break.
Molly found a dead body.
She / Her
A colossal yet breakable-looking and transparent wall. EDIT: I didn't put too much thought into it![[lol]](https://static.tvtropes.org/pmwiki/pub/images/lol2v12_4863.png "[lol]"){kind=small}
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Edited by RandomTroper123 on Oct 20th 2022 at 4:14:29 AM
Dapper Hat
One way glass, like you would see in a police interrogation room.
The inanimate object equivalent of Cthulhu.
A one way mirror that looks exactly like the 4th wall of the room from the characters perspective.
It would look like what we see when we look to an audience from a theater stage, except more... surreal.
The Draftsman of Doom
I would imagine it looks like the view from inside the screen or page.
Feels good, don't it?
An invisible, inperceptable, moving wall, moving based on angle. Those who discover it have their minds broken by the eldritch mind-bending nature of it (Such as Jevil)
You!
Wacky funhouse mirror
Signature, schmignature!
A crewmate from Among Us
No "Bowser's Fury" questions please. I haven't played it yet.
The opposite side of a TV screen.