Yoshi's Egg

In most games featuring Yoshis, Yoshi Eggs are involved. Yoshis are known for being capable of laying eggs at will. They usually contain a Baby Yoshi or an item inside. The Yoshi Egg is also Yoshi's signature emblem in various games.

Super Mario World
When Mario or Luigi find one of these in Super Mario World, a Yoshi hatches and it acts as a steed, allowing Mario and Luigi to ride it. Yoshi can swallow enemies with the or  button. If Mario or Luigi find another Yoshi Egg while an already-present Yoshi is nearby, a 1-Up Mushroom will emerge instead, rather than another Yoshi. Mario will also rescue a yellow egg from each Castle he encounters. These eggs do not hatch until the end of the game. According to the story, Bowser trapped all the Yoshis in eggs. Strangely, all of the Yoshi that hatch from the eggs collected from Catsles are all different colored Yoshis, yet all of the eggs are yellow.

There are also multi-colored Yoshi eggs that appear outside of item boxes in the Star World levels. Approaching one of these will cause it to hatch into a baby Yoshi, its color varies on the color of the egg. In Super Mario Advance 2, the remake for Mario World, the bros. can find a Yoshi Egg of any color in a Question Block after using that Yoshi in the Star World.

Super Mario Bros. Deluxe
Yoshi Eggs also appear in the challenge mode of Super Mario Bros. Deluxe. In challenge mode the player must collect Red Coins or eggs. Red coins can be found as normal, like regular coins, but Yoshi eggs are more difficult to find. Yoshi eggs may only be found from hidden blocks throughout the level. Collecting both in a certain amount of time will affect the score. If the player collects the eggs fast enough, they may earn a reward.

Super Mario Advance
In the Super Mario Advance version of Super Mario Bros. 2, Yoshi eggs can be collected after the game is completed. This is known as the Yoshi challenge. Two Yoshi eggs per level can be found in Subspace, in the places where Mushrooms would normally be found. Thus, only three hearts is the maximum capacity during the Yoshi Challenge. The player also must successfully beat all the levels without losing lives. Dying will cause the player to lose the eggs they collected for that level, and they have to collect the eggs again. The Yoshi eggs will hatch once all of them have been found for a world.

Super Mario Sunshine
Yoshi Eggs appear in Super Mario Sunshine as well. Shadow Mario possesses one in Delfino Plaza and the player needs to stop him by spraying him with F.L.U.D.D.. Then the player needs to get the correct fruit indicated by a small thought bubble over the egg. When the correct fruit is brought to the egg, a Yoshi will hatch from it. However, if Mario brings the wrong fruit to Yoshi's egg, the egg will turn from side to side, as if trying to say "no".

Yoshi eggs appear in many levels, and are sometimes needed to finish a level. When Pinna Park is invaded by a Snooze-A-Koopa colony, the Yoshis residing there flee, insulted by the appearance of creatures who resembled Yoshi eggs. Completing the episode in Pinna Park will cause the Yoshi eggs to appear all over Isle Delfino.

Super Mario 64 DS
Yoshi eggs appear in Super Mario 64 DS as a helpful projectile for Yoshi. They can be acquired by eating enemies and swallowing them to turn into Yoshi eggs. Unlike Yoshi's Island, Yoshi can only carry one egg at a time. If Yoshi wants to stick his tongue out again, he must throw his egg in order to eat again.Yoshi Eggs will home enemies in screen and can bounce off enemies to hit another. If Yoshi swallows a wooden crate, the egg will take in form as a crate.

Eggs also appeared in both of Luigi's minigames, the Mario Slot and the Super Mario slot. Among the other slots, a Yoshi Egg is in them. Getting three Yoshi Eggs in a row will earn the player five coins.

The original Super Mario 64 did not feature any Yoshi Eggs, but an unused Egg texture can be found in the game's coding.

New Super Mario Bros. Wii
Yoshi returns in this game, hatching from a Yoshi egg when a player hits the block. The Yoshi egg acted in a similar manner in Super Mario World, which Yoshi also hatches from an egg that got spawned from a certain block. However, no Yoshi eggs could make 1-up Mushrooms. Instead, Mushrooms popped out of Yoshi Eggs. Yoshi Eggs also come out briefly during the opening scene of Peach's birthday. It is notable that there is a larger than usual Yoshi Egg next to Mario wrapped in a bow.

Super Mario Galaxy 2
Yoshi eggs appear in Super Mario Galaxy 2, in nest-like holes located in several galaxies, waiting for Mario to break them. If Yoshi is hurt or lost, he will retreat into his egg and must be freed again. Yoshi's egg also resides on Starship Mario.

The original Super Mario Galaxy did not feature Yoshi Eggs as actual interactive objects, but there was a planet in the Good Egg Galaxy which resembled a Yoshi Egg.

New Super Mario Bros. U
Yoshi Eggs are set to reappear in the upcoming Wii U game New Super Mario Bros. U. The eggs the Baby Yoshis spawn out of appear to have the color palettes of the egg switched.

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

Mario & Wario
In World 2 of the game, the thing that Wario puts on Mario's head is half of a cracked Yoshi Egg.

Super Mario World 2: Yoshi's Island
Unlike games that preceded it, Yoshi Eggs in Super Mario World 2: Yoshi's Island are used as projectile weapons that are used by aiming and firing. Yoshis can lay eggs by swallowing enemies. Yoshis can also obtain these eggs by hitting an Egg Block that contains an unlimited supply of Yoshi eggs. The Yoshi can only carry 6 eggs at any time. 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. Each of the eggs, except the green egg, has a different effect.

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. In the tech demo, the Health eggs have light green smiley faces on them.

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

Yoshi's Island DS
Yoshi eggs act the same way in Yoshi's Island DS. 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.)

Super Smash Bros. series
Throughout the series, one of Yoshi's special moves lets him swallow opponents and turn them into eggs, temporarily stunning them. Also, his defensive move makes him encase himself into an egg.

Eggs are a throwable weapon in Super Smash Bros.. A single Yoshi Egg appears in one of the events of Super Smash Bros. Melee. In it, 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. In the twelfth event "Sleeping in the Eggs" in Super Smash Bros. Brawl, Yoshi must simultaneously capture Kirby and Pikachu inside Yoshi Eggs.

Additionally, throughout the entire Super Smash Bros. series, Yoshi enters stages at the beginning of every match by hatching from a Yoshi Egg.

Super Mario Kart
An egg is used as a projectile as Yoshi in Super Mario Kart. Only the computer may use the egg and Yoshi has an unlimited supply of it. The egg is like a "special" item that most of them are exclusive to other computers.

Mario Kart 64
Only one egg makes an appearance in Mario Kart 64. It is located in Yoshi Valley, near the last stretch before the grassy area and the finish line. The Egg moves about in a circular pattern. When a player runs into it, the Egg will smash the player, similar to when a player gets smashed when they are tiny. Manoeuvring around this particular egg is difficult due to its tremendous size.

Mario Kart: Double Dash!!
In Mario Kart: Double Dash!!, the Yoshi Egg is a special item, exclusive to Yoshi and similar to Birdo Egg. When thrown, the Egg will home on the next place racer. If a player uses it while first, the egg will just follow down the track and break. Unlike the Red Shell, there is a certain amount of distance an egg needs before it cracks, and the red shell is continuous until it either goes off the course, goes into a wall, or hits the player. When it breaks, three random items will get thrown out, which can be Green Shells, Mushrooms, Bananas, Fake Item Boxes, Stars, or Bob-ombs.

Mario Kart DS
In Mario Kart DS, the only appearance of an egg is in one of Yoshi's vehicles, called the Egg 1. It is a very simple kart, consisting of an egg, wheels, and tail pipes sticking up. It has very high acceleration and handling, but low weight and speed, much like the other lightweight vehicles. It is also one of the two vehicles that is most commonly used online, by snakers (the other is the Dry Bomber).

In the Yoshi Falls course, the setting is in a road circling around a lake. In the middle of the lake contains a giant Yoshi egg. However, it is just for looks and doesn't serve any purpose whatsoever, unlike the egg in Mario Kart 64.

Mario Kart Wii
The Yoshi Egg appears only as an emblem in the karts and bikes when Yoshi's chosen. There is also a giant Yoshi Egg that appears in the retro course Yoshi Falls, taken from Mario Kart DS.

Mario Kart 7
The Yoshi Egg is once again Yoshi's emblem and it also makes small appearances throughout courses. The Egg 1 also comes back from Mario Kart DS.

Mario Party series
In most Mario Party games, the Yoshi Egg appeared as one of the objects in various minigames. Yoshi and Birdo's signature orb in Mario Party 7 is the Egg Orb, which transforms any Character Space (excluding Koopa Kid Spaces) into a Yoshi Egg.

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

Mario & Sonic at the London 2012 Olympic Games
Yoshi Eggs serve as the objectives of the Dream Equestrian in Mario & Sonic at the London 2012 Olympic Games. In the event, players must race to the finish line, carrying a wagon full of seven colored Yoshis while avoiding obstacles. If a egg falls off the wagon, a 10 second penalty will added to the player's time upon completing the event.

Appearances in Other Media
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 Mario & Luigi: Bowser's Inside Story, the Fawful Guys have an attack where a fawfulized Yoshi throws them in a yellow Yoshi egg.
 * A Yoshi egg can be received in Animal Crossing: City Folk for 1,000 shop points.