Here's an image I found on Reddit:
Apparently, it's a tin tray, and it's official judging by the © in the bottom right. Also, here's a comment that addresses everything of note:
[quote author=/u/deepthaw]Does that cloud have a barcode for a mouth?
What kind of bizarro dimension does Luigi's room reside in? I don't recall any twisted carnival horror hallways like that in the games.
Has Bowser seen an eye doctor lately?
Are two two different distinct species of Toad? Those that have no legs and wear pants, and those with legs but don't wear pants?
That phone booth is clearly floating several feet above the floor, going by the line that's supposed to represent the border between floor and wall. Mario's kind of a dick if he makes his star-friends pay to use a payphone when they're visiting.
Mario's dad has seen some stuff. You can tell.
Continuing the "everything is animate" trend, the television antenna has eyes. And seems weirded out.
Mario's TV apparently has a screen made of paper.
That NES advantage, other than being bizarrely huge, has a lot of extra buttons. Mario's in the arcade stick modding scene, I see.
It's interesting that the flower pot, but not the flower has eyes and a face.
That goomba totally has arms.
Is that a Koopa Troopa on top of the phone booth? Why is he holding a flag? Maybe that's a stuff trophy of one of the many flagpoles Mario has conquered.[/quote]
I kinda want someone to go completely in-depth and explain every detail that this thing got wrong.