Question Coin

From the Super Mario Wiki

A Question Coin is a special Coin in Super Mario Galaxy. When one is obtained one of the following occurs:

• A Mario theme will play and a line of musical notes will appear for Mario to collect, usually causing a 1-Up Mushroom to appear.
• An accumulation of Star Bits or Coins will appear for Mario to collect.
• A power-up will appear.
• Another question coin will appear

They appear in few stages, like Good Egg Galaxy.

Coins Mario series Ace Coin • Advance Coin • Beanbean Coin • Blue Coin • Dragon Coin • e-Coin • Evil Coin • Frog Coin • Golden Coin • Large Coin • Mario Coin • Pianta Token • Purple Coin • Question Coin • Red Coin • Silver Coin • Slot Coin • Star Coin Yoshi series Character Coin • Coin • Heart Coin • Red Coin Wario series 100 Gold Coin • Gold Coin DK series Coin • Banana Coin • Bear Coin • Bonus Coin • DK Coin • Kremkoin • Nintendo Coin • Taj Token SSB series Smash Coin