Everything Wrong With The Amazing World of Gumball

EWW: The Mystery

Gumball and Darwin are at school. Gumball is opening his locker
Gumball: I think cheese is better than cake, because you can have cheesecake, but you can't have cake cheese.
No twelve-year-old would ever actually think this +1

Also, so many things are turned into cake these days that cake cheese very easily could be a real thing Thus Gumball's point is invalid anyway. +1

Lucy Simian: Oh, my sweet Nigel. Who would shave you, paint you, wrap you in toilet paper, and shut you in Watterson's locker?! Who did this?
Ms Simian, the teacher notoriously known for hating Gumball, didn't immediately blame him for this. Especially considering Principal Brown was in his locker. She would absolutely take that as definitive evidence it was him. +1

Lucy Simian: And if the culprit hasn't owned up by the time I get back, you're all in detention!
Miss Simian slams the door of the classroom and leaves. Bobert can be seen in the background standing still on the stairs as the camera zooms in on him slightly.
A nice subtle bit of foreshadowing here, and pretty easy to miss too. -1

Bzanana Joe: Oh, c'mon, it was obviously Gumball!
Tobias​​​​​​: Yeah! Brown was found in his locker.
Everyone looks angrily at Gumball. Darwin then follows suit
They assume simply because Principal Brown was in his locker that it had to have been him, even though it would make no sense for Gumball to stuff Nigel into his own locker if this were the case. That would do nothing except incriminate himself, and even in Season 1 he's not that stupid. +1

Also. Darwin and Penny look over at him accusingly even though they would absolutely be the first two people here to jump to his defence in a situation like this. +1

Gumball: Guys, I didn't do it. But I'm gonna find out who did. And I think I know just how. Whoever did it, raise your hand!
No one raises their hand
He expected this to work. +1

Gumball: Okay, whoever didn't do it, raise your hand!
Everyone raises their hand, except Alan. They all look at him
And this. +1

Alan​​​​​​: What?
Gumball: Aha! So you did it! Pokes him
Alan​​​​​​: Bumps Gumball back Dude! I don't have any hands!\
I'm not sure if this was an intentional callback to the no-hands joke from The Third or not, but either way it works as one which I love as it's very rare for the show to ever do callbacks, at least in Season 1. -1

Penny: Aren't you supposed to... like... look for clues or something?
They're just letting Gumball take charge of the investigation now even though he himself is not only a suspect, but the prime suspect. +1

A big spotlight shines at Penny and everyone looks at her and gasps, surprised
Random dramatic light is random +1

Leslie​​​​​​​​​​​​​: Gumball, have you seen your yearbook photo?\
Leslie holds up a yearbook and points at Gumball's photo. He has a derpy pose and face on the photo
This small bit acts as a nice unintentional setup/foreshadowing to The Photo, way later on in Season 2, which is so cool! -1

Gumball: It was you!
Penny: Gasps
Gumball: But I forgive you, because I am madly in love with you too.
Penny: Yeah, well, that's not quite what happened.
Flashback to yesterday at the school stairwell, Penny hangs her finished painting
Penny: Voice-over I had finally finished my painting of the cheerleaders, and I went to hang it in the stairwell. I guess it was still wet, and I must have got paint on my pompoms.
Flashback ends
Gumball: And did anyone see you supposedly hang this alleged painting in this so-called stairwell?
Penny: Yeah. You did.
Flashback begins. Penny hangs her finished painting, as Gumball comes around the stairwell
Gumball: Hey, Penny! I love you! Your painting! Your painting. I love your painting.
He outright admits his feelings for Penny, here and earlier when he said he loves her on the stairwell, yet it still takes until Season 3 for them to actually get together. Aka...