Yoshi's Egg

In most games featuring Yoshis, Yoshi eggs are involved. Yoshis are known for being capable of laying eggs at will, sometimes with Yoshis or items inside.

When Mario or Luigi collect one of these in Super Mario World, a Yoshi hatches and they can ride it. On Yoshi, they can swallow enemies with the X or Y button. In Super Mario World 2: Yoshi's Island, Yoshi lays eggs by swallowing enemies. In Yoshi Touch and Go, he lays eggs when he collects fruit. The eggs can be used to collect items and defeat enemies. His eggs can be used as a weapon in Super Smash Bros. In the Mario Kart games, the egg is used to hit your enemies in front of you and send out random items, like a Super Mushroom, in the air.

A recent video of the upcoming Super Mario Galaxy reveals that a planetoid obviously based after a Yoshi egg will appear.