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.

Super Mario World
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. If Mario or Luigi get another Yoshi Egg and the one of the brothers have a Yoshi; a 1-Up Mushroom will pop out for a bonus for keeping the Yoshi.

Super Mario World 2: Yoshi's Island
In Super Mario World 2: Yoshi's Island, Yoshis can lays eggs by swallowing enemies. Yoshis can also obtain these eggs by hitting a Egg Block that contains an unlimited supply of Yoshi eggs, the Yoshi can only carry 6 eggs. Eggs can also fall into Tulips in this game, resulting in the Tulip spitting out stars. There is the standard green egg, Yellow Eggs, Red Eggs, and Flashing Eggs. All of these eggs, except the green egg have a different effect.

Super Mario Sunshine
Yoshi Eggs appear in Super Mario Sunshine as well. Shadow Mario has one in Delfino Plaza and the player needs to stop him by spraying him with FLUDD. Then the player needs to get a fruit. A certain one needs to be gotten, and it will be the one in a small thought bubble over the egg. when gotten, a Yoshi will come out that Mario can ride around. These eggs will then appear in many levels, and are sometimes needed to finish a level.

New Super Mario Bros. Wii
Yoshi eggs appear in New Super Mario Bros. Wii. In it they will come out of Blocks (depending on the how many players) like they did in Super Mario World (without Red & Blue Yoshi). it has Green, Pink, Light Blue, and Yellow Yoshi eggs.

Wario Series
The treasure for the third level "Invade Wario Castle" in Wario Land II resembles a Yoshi Egg.

Yoshi's Story
Yoshi eggs are laid automatically in Yoshi's Story, but are still used as projectile weapons. Unlike in Super Mario World 2, the eggs hold no special effects; although eggs thrown by the White and Black Yoshi have more of an explosive impact.

Yoshi's Island DS
Yoshi eggs act the same way in Yoshi's Island DS, there are also yellow eggs, which produce two coins if one hits an enemy or a cloud, and red eggs, which produce two stars. Flashing eggs make a cameo in Secret 5 as a tracker for which Easter Egg the player is on. but are not usable in the game (in the original Yoshi's Island, they provided a red coin.)

Yoshi Touch and Go
In Yoshi Touch and Go, he lays eggs when he collects fruit. The eggs can be used to collect items and defeat enemies.

Super Smash Bros. Series
These eggs can be used as a weapon in Super Smash Bros.. A single Yoshi Egg appears in one of the events of Super Smash Bros. Melee. In it, the player, as Yoshi, must keep the Yoshi Egg from breaking. If it is broken, the player fails. If time runs out and the Yoshi Egg isn't broken, the player wins.

Mario Kart Series
In Mario Kart: Double Dash!!, the egg is a special to Yoshi, Petey Piranha, and King Boo. When thrown, 3 items pop out of it and land on the ground. Birdo's Egg works exactly like this item, but has pink spots instead of green.

Mario Pinball Series
In the Game Boy Advance video game Mario Pinball Land, a Yoshi Egg act as a pinball that Mario could buy at the shop.

Comics
In the Club Nintendo comic "Ostern im Schwammerlland", the Easter bunny dropped a Yoshi Egg, out of which Yoshi emerged.

A Yoshi Egg played an important role in the comic "Mario in Mariozilla", published in the same magazine. In this story, some fog coming out of Kamek's broom shrinks the Magikoopa and Mario to ant-size. When they sit on a blade of grass waiting for help, Yoshi swallows them. All attempts to get the two out of Yoshi's mouth fail, but ultimately Dr. Light gets the idea that Yoshi laying an egg could be the solution to the problem. Yoshi obviously has difficulties doing so, but two hours later, he finally lays an egg. Light breaks it up and indeed Mario and Kamek come out of it.

Trivia

 * In the Yoshi's Story tech demo strangely the "Health" eggs had light green smiley faces on them.
 * In Mario & Luigi: Bowser's Inside Story, the Fawful Guys have an attack where a fawfulized Yoshi throws them in a yellow Yoshi egg.
 * In Super Mario 64, an unused Yoshi Egg texture can be found in the games coding.
 * A Yoshi egg can be received in Animal Crossing: City Folk for 1,000 shop points.
 * In Pokémon Ruby and Sapphire and other Pokémon games latter released, the Pokémon eggs bear a resemblance to a Yoshi Egg.
 * One of the treasures found in Wario Land 2 looked just like a Yoshi Egg.
 * Although Yoshi Eggs don't appear in Super Mario Galaxy, there is a planet that looks just like a Yoshi Egg in the Good Egg Galaxy.