Creepiest Mario Level/Area

[Ray Trace]

I hate jump scares and the piano is no exception @~@

 

[PeskyPlumbers64]

How about the hidden ghost in 3D Land? That genuinely creeped me out the first time I saw it, mostly because I wasn't expecting it.

 

[Ultraluigi]

big boo's haunt
simply because i played that game when i was 5, and i did not expect the piano.

 

[FoxWolf64]

Big Boo's Haunt. It just has a feel about it that's just completely unsettling. Yes, there are other haunted levels in other games, but this one just spooks me. Everything about it.