Bonus Coin (Super Mario World)

The Bonus Coin is a special and rare coin that appears in Super Mario World. It's a normal yellow coin with a slightly more rounded shape and with a smiley face on it.

Super Mario World
In Super Mario World and Super Mario World: Super Mario Advance 2, when Yoshi eats two Pink Berries, he will hatch an egg with a Yoshi Cloud inside, which then hovers above Mario and pops out ten Bonus Coin, after which it flies away. If Mario manages to collect all ten coins before they faze through the ground after bouncing once on it, the Yoshi Cloud will reward him with a 1-Up Mushroom.

Super Mario-kun
In chapter 8 of volume 2 in Super Mario-kun, while fighting a Jumping Pumpkin Plant, Mario falls on Yoshi, making him pop out an egg. Inside, a Yoshi Cloud appears. Mario jumps on it and eats the Bonus Coins, becoming the big-headed Nikoniko Mario, scaring off the enemy.

Trivia

 * In the Beta of Super Mario World, the Bonus Coins were originally designed with a star on it. This appearance will be later used for the coins in Super Mario 64.