Quoting VGcats is the best.
It had looked like a magic truffle, so of course he'd eaten it.
Big mistake. The world almost instantly shifted to something that at best resembled a mash up of Moonside and Magicant. The plants kept singing about facing the sun and smiling, and guys in surfer shirts kept warping them from one place to the next.
Ness found a mailbox. When he opened it, letters and packages from his mom came spilling out. They kept spilling out, building up past his ankles, then his knees, then his middle. They kept coming. The thought vaguely passed his mind to close the box, but his body wasn't responding. The mail was up to his shoulders now. Now his nose, and soon, all that was left was a red hat atop a mountain of mail.
"Why didn't you call home more?" the letters said all at once. "Tracy baked you cookies!" The packages spit stale cookies at him. A gust of wind came and blew all the letters and cookie crumbs away. Ness's hat landed on his head with a splat. It's skin broke like a tomato's and it ran down Ness, turning him completely red.
"Why aren't you blue???" A man in a hood demanded, brandishing a paintbrush. "You must be colorblind! Hey guys come here and help me with this kid!" Several other hooded men came running over and dumped cans of blue paint all over Ness. He could feel the paint drying almost instantly, and was finding it harder and harder to move.
Then he couldn't at all, because he was diamondized. He fell onto his back and could only stare at the pink sky. Poo looked down at him, drinking a bottle of water.
"Sorry, no PP." he said as he was pulled up by the UFO's beam.