An egg is an item found in the Mario series. They can be used as projectiles, used mainly by Yoshi to help Mario on his quest or in Super Mario Bros. 2, a projectile in order to defeat Birdo, who spat them out. In other games, they are a helpful item or a hindering item depending on the game and the time.
Super Mario series
Super Mario Bros. 2
The egg's first appearance by game was Super Mario Bros. 2 in a dream place called Subcon. Eggs appeared as a projectile when fighting Birdo when she spits them out to attack. In order to defeat Birdo, the player must stand on the egg while it's flying and pick it up and toss it back to Birdo. In later boss fights with Birdo, she may spit out fireballs instead of eggs and in the last Birdo fights, she spits out only fireballs and the player must use projectiles nearby to attack Birdo. Robirdo also shoots large eggs out of its mouth-like cannon and attacking Robirdo was in a similar matter to attacking regular Birdo.
Super Mario World
Yoshi eggs make a small appearance in this game. When Bowser occupies Dinosaur Land, he imprisons several of Yoshi's friends in eggs. There are two types: Eggs that produce ride-able Yoshis and eggs containing the dinosaurs rescued at the end of each world. The eggs that produce ride-able yoshis are found in the Star World.
Super Mario Galaxy
A galaxy named Good Egg Galaxy is the first galaxy in Super Mario Galaxy. There is a planet shaped like a Yoshi Egg, making it a cameo appearance for Yoshi. Also, when Mario or Luigi cracks an egg when landing on the last planet in the mission "Dino Piranha", a Dino Piranha will come out of the egg, wandering around at first. When Mario destroys it with the Dino Piranha's tail, the tail destroys the egg, leaving Dino Piranha in a rage.
An egg could also be found in Melty Molten Galaxy, but that egg contained Fiery Dino Piranha, which behaved in almost the same manner as Dino Piranha, except with a fiery tone.
Super Mario Galaxy 2
In Super Mario Galaxy 2, Yoshi would hatch from his egg if Mario jumps on it. Also, Peewee Piranha hatches from a giant egg, as well as Dino Piranha and Fiery Dino Piranha (who returned from the previous game) in the Boss Blitz Galaxy.
Super Smash Bros. series
In all Super Smash Bros. games, eggs have made an appearance as an item. They can be thrown at opponents, or eaten for health. They are sometimes released by the Pokémon Chansey. In Super Smash Bros. Melee's Mushroom Kingdom II stage, Birdo appears in her original sprite from the Super Mario All-Stars version of Super Mario Bros. 2, shooting eggs. These eggs travel in a straight line and cause minimal damage, but they can be picked up and thrown for considerably more damage. A spotted Yoshi Egg also appeared once in an Event Match in which Yoshi must protect it from other foes.
Eggs also serve as special moves for Yoshi. Up special will make Yoshi throw one egg at a time in the air. Yoshi has an unlimited supply of eggs and he can aim them while throwing them. Yoshi's Side Special will make him go in a egg and roll around at high speeds, making it powerful, but hard to control. Yoshi also has an egg for a shield, unlike everyone else, who has a bubble.
In the SNES version of Wario's Woods, Creature Eggs are items that can be achieved whenever Toad performs a "breakfast" combo move in the vs. mode. The breakfast move is performed whenever Toad clears multiple rows/columns/diagonals of monsters at once with one bomb. At this point of time, a falling egg will appear on the side of Toad's opponent. Upon hitting the ground, this Creature Egg would hatch into any type of monster of varied colors. After the Creature Egg hatches, an additional row of monsters of one color will rain on his opponent. Whenever Toad performs a three way breakfast combo will send two eggs instead of one. While the eggs can be prevented from hatching, it is difficult to do so as it must be done by matching an entire row of monsters with the color of the egg.
In Paper Mario, Eggs restore five HP. Eggs are quite rare in the game, Egg appears when checking the grass in the first area of Mt. Rugged where there is a train station, and it also appears by pulling a vine in Jade Jungle, in an area behind the Raven Statue. Eggs also appear in the kitchen of Princess Peach's Castle and are used to make Strawberry Cake for Gourmet Guy. In this case, it's item description reads: Newly laid eggs.
Mario Party series
Mario Party 5
In Mario Party 5, the egg only appears in Super Duel Mode, called the Egg Body. According to the description, it is made out of Yoshi eggs. This body is durable and it increases a machine's offensive and defensive capabilities. The Yoshi opponent in the tournament uses this body.
Mario Party 7
An egg appears in Mario Party 7 in form of the Egg Orb. Only Yoshi and Birdo can acquire it and use it. When used, the Egg Orb will activate and will last the turn. If Yoshi and Birdo passes a trap space while the Egg Orb is in effect, Yoshi and Birdo will turn it into an egg and the orb will become theirs to use. The Egg Orb can also deactivate Koopa Kid spaces, but it will not be available for use.
Mario Party Advance
Mario Party DS
An egg made a brief appearance in the Mario Party DS mini-game Memory Mash. The player must collect matching cards while flipping them over with a ground pound. Among the cards, there is a Birdo Egg and a Yoshi Egg.
Mario & Luigi series
Mario & Luigi: Superstar Saga
Eggs appeared as Neon Eggs in Mario & Luigi: Superstar Saga. In order to obtain them, Mario and Luigi must find hidden bean fruits under the ground. After obtaining them, Mario and Luigi must feed the bean fruit to a hungry Yoshi. After eaten, the Yoshi will lay an egg corresponding to the color of the Yoshi. There are seven different eggs in all and completing the collection will earn Mario and Luigi a piece of the Beanstar.
Mario & Luigi: Partners in Time
In Mario & Luigi: Partners in Time, Yoshi Eggs can only be found in Yoshi's Island. There was a strange looking egg on display and out came a Yoob that was hungry for the Yoshis. After the Yoshis are trapped in eggs inside the Yoob, Mario, Luigi, and their baby counterparts must shut the Yoob down in order to stop the factory process that is going inside. Sunnycide, a boss, hatches from an egg and uses eggs to attack the Mario brothers. They must crack the eggs open in battle to free Yoshis trapped inside them, so they can bring up a Chomp Rock to make Sunnycide flip over.
There is also an unused Yoshi Egg.
An egg called a Smash Egg can be obtained by either defeating enemies or purchasing from shops. When used, the person who selected it in battle will kick the egg into an enemy. The big brother may use it to attack the enemy while the babies may jump on it to make the egg faster and stronger. When bounced enough times on an enemy, the egg will crack, sometimes having an item inside it. The Smash Egg is first found in Yoshi's Island.
Mario Baseball series
Mario Superstar Baseball
Eggs take in form as power swings in Mario Superstar Baseball. Used by Yoshi and Birdo, with the names, Egg Ball and Weird Ball, they are unique power swings. While most star swings go in one direction and bounces once before stopping, the egg balls will bounce about erratically, making it difficult to catch the ball. What can make it more difficult is that it may bounce on the field and then bounce to the foul zone. However, in other cases, the ball will be caught right when it lands. When used while pitching, both balls will move about erratically also, making it very hard to hit it. Some cases, however, it may be called as a ball.
An egg may be obtained by the Toad Shop in Challenge Mode. To do so, the player must be or recruited Yoshi in order to purchase it. Same goes to Birdo and the Pink Egg. After either of the eggs has been purchased, it gives Yoshi or Birdo a permanent ability to use the Egg Ball or the Weird Ball. Both can be bought for 200 coins and buying it will result a star mission star for Yoshi and Birdo according to which was bought.
Mario Super Sluggers
The egg-based Power Swings make a return into Mario Super Sluggers. They both acted nearly identical to the preceding game, but they got different names for the shots and swings. Yoshi's Egg Ball is now called Rainbow Swing and Rainbow Ball while Birdo's Pink Egg is now called Cannon Swing and Suction Ball. The appearance of the Birdo Egg also changed; from a pink spot pattern to a pink ribbon pattern depicting Birdo.
Donkey Kong Country series
In Donkey Kong Country 2: Diddy Kong's Quest and Donkey Kong Country 3: Dixie Kong's Double Trouble, Squawks the Parrot can shoot eggs out of his mouth. By doing this, he can knock out enemies that are in Diddy Kong and Dixie Kong's way. In order to have Squawks shoot out an egg, the player must press the button on the Game Boy Advance. In only Donkey Kong Country 2: Diddy Kong's Quest, eggs can be found on the levels Krow's Nest and Kreepy Krow, in which Krow, drops eggs on the Kongs, attempting to harm them.
Types of Eggs
The Yoshi Egg is the most common type of egg in the Mario series. They are generally found everywhere, spawning from blocks to laying them from Yoshi. Yoshi eggs usually serve for a benefiting purpose especially for Yoshi since he couldn't go on his quest in most of the games in the Yoshi series without the use of eggs. Other Yoshis use them too, and some lay eggs corresponding to the color of them, as seen in Mario & Luigi: Superstar Saga. The Yoshi Egg is also Yoshi's signature emblem in various games.
Although recent games have proven that Birdos can spit pink Yoshi Eggs, most Birdo Eggs are non-spotted. A Birdo will spit Birdo Eggs out of its cannon-like snout, and uses the eggs like bullets. The player can jump on these to get a free ride, and sometimes, like in level 4-3 of Super Mario Advance, a Birdo egg had to be ridden. Birdo also uses it as an item in Mario Kart: Double Dash!! and it acted the exact same as the Yoshi Egg. A Birdo Egg typically has pink spots, but as seen in Super Sluggers, the Birdo Egg instead has pink ribbon patterns all over it instead of spots.
Found only in the Boggly Woods, Mystic Eggs are from an unknown creature. Nobody knows where to find them except the Puni girl, Petuni. For a certain favor, Mario can obtain Mystic Eggs from Petuni during the events of Paper Mario: The Thousand-Year Door. Like in its prequel, the egg recovers five HP and may be used in all sorts of recipes.
The Smash Egg made its only appearance in Mario & Luigi: Partners in Time. It resembles a Yoshi egg, except it has yellow stars instead of green spots. The Smash Egg was used as a Bros. Item that was first obtained in Yoshi's Island. It could hit multiple opponents at a time and it may release an item after it hits the enemies enough times.
Creature Eggs made their first (and only) appearance in the SNES version of Wario's Woods. Creature Eggs appear whenever Toad performs a "breakfast" combo move in the vs. mode. Upon landing on the opponent's side, the creature eggs will hatch into any one of the monsters of assorted colors. These eggs can be prevented from hatching, though they must be matched up with the monsters of their same color in order do so. Creature Eggs bear a strong resemblance to Yoshi Eggs.
Trophy Information from Super Smash Bros. Melee