No no no, see, the muffin is made out of fragments of the Rainbow of Light itself. It gives a pony superpowers like enhanced magic (if you're a unicorn, other ponies just get telekinesis), flight (if you're already a pegasus, it allows any pegasus to do a Sonic Rainboom), super strength (all ponies), and other standard superpowers.
However, it tastes like crap. Why? Because Derpy helped make it, and she doesn't know what went wrong.
Also, the more you eat of it at once, the stronger you get. And it always regenerates after the powers wear off, so it can be used multiple times. And if you eat all of it at once...
Well, let's just say whatever force of evil that's terrorizing the land is about to... (sunglasses) taste the rainbow, motherbucker.
There will soon be a throw down match between the three on who eats it. Sadly though, the muffin will be a casualty in the fight. Great picture, muffin must look good as it has both of Derpy's eyes on it.