Glad you like it. :)
The joke is that once the mushroom runs into the pipe, it will have no choice but to turn around and run straight back into Mario, which is why Mario doesn't look concerned about chasing after it. (Mushrooms simply bounce off of objects and start going the opposite direction that they were headed in the game.)
So if I don't have a Mario Pixel, so will my gallery be erased? Cool. 
Very charming, I love the details, the green pipe and the little cute innocent mushroom runnning away from Mario, he looks like a creep.
i have three, that counts?