Magic Coins are secrets that happen when you collect a blue or normal Coin. Every time you collect a coin there is a small chance (less than 1%) for you to get a Magic Coin. When you find a Magic Coin a message will pop up in the chat announcing that you have just found a Magic Coin.
When you get a Magic Coin, you will always get +1, +5, +10, or +15 max Energy. It used to be possible to collect 30 max energy from a Magic Coin. There is a chance that when collecting a Magic Coin you will get the wizard smiley, the magic block package, and sometimes you can also get a refill of your energy.