For reasons better not gone into, Art Attack has a background in dream interpretation, the study of the meaning behind objects that appear in our dreams. You thought that your brain was just being funky when it had you downing a bowl of raisins with Kesha and Cornelius from Planet of the Apes, but it really means that something sinister is working against you. That's the raisin bit, anyway. No idea what Kesha and the ape are doing in your head.
Another passion is everything involving Super Mario, and like most people we've always wondered why the hell a flower gives you the ability to shoot fire, or a feather turns you into a crap, Italian version of Superman. Dream imagery seems as good an explanation as any, and actually does sort of make the whole system a little more understandable.
Originally called the Magic Mushroom until someone had a little talk with Japan, we always assumed that the inspiration for a mushroom that increases your size came from Alice in Wonderland, but according to Shigeru Miyamoto, the mushrooms were actually inspired by the concept of mushrooms being associated with magical worlds. Who are we to argue with the man who invented fun? They remain the most constant staple in the games, with a variety of effects, but mostly the getting bigger thing.
The mushroom symbolizes unhealthy vices and poor decisions.... Such as, we don't know, constantly running after a princess that can't stay un-kidnapped for five minutes instead of really putting time and effort into your plumbing practice. Also, when Bowser Jr. claimed Princess Peach was his mom, her response boiled down to "Really? Me? Okay?" so poor choices seems to be the norm even in the aristocracy of the Mushroom Kingdom.
On the plus side, eating mushrooms in a dream can be a mark of confidence and power, and Mario must have that in spades if he's man enough to take the sloppy seconds of a giant turtle dragon.
By eating a special flower, Mario can hurl fireballs that bounce along the ground. Originally, Mario was going to come straight out of Compton and use a gun, but in the end it was fireballs courtesy of posies with faces.
In dreams, flowers symbolize pretty much what you would expect: beauty, tranquility, happiness, love, etc. Not exactly the best item to give you a devastating weapon. However, flowers growing from barren soil -- and what's more barren than a block of brick? -- is a sign that your energetic and cheerful nature will help you overcome obstacles. That's pretty damned spot-on.
On the other hand, if you see a fireball in your dreams it means you're on a hideously self-destructive path. Another indicator that perhaps Mario's chosen profession of Koopa stomping isn't the most constructive thing he could do with his life.