Spiny Egg

Spiny Eggs, originally known as Spiny's eggs, are the projectiles thrown by Lakitus. Spiny Eggs are small, usually red balls covered in spikes. Once they touch the ground, they turn into normal Spinies. Despite its name, a Spiny Egg would appear to not be an egg at all; it seems to simply be a Spiny rolled up into a ball. While in this state, they can be defeated when touched by a Star, burned by Fire Mario's fireballs, attacked by Raccoon Mario's or Tanooki Mario's Tail attack, etc.

Super Mario Bros
Spiny Eggs debuted in the original Super Mario Bros.. In this game, they were of a more elongated shape than later appearances.

Super Mario Bros. 3
Super Mario Bros. 3 included the original red Spiny Egg, colored orange in the Super Mario All-Stars remake, and introduced a green Spiny Egg, which doesn't hatch, but slowly rolls along the ground chasing Mario. The Spiny Eggs in this game were spherical.

Super Mario World
In Super Mario World, Spiny Eggs are colored orange, like the Spinies of that game. Along with normal Lakitus, they can be thrown by Fishin' Lakitus and Lakitus found within pipes.

Super Mario 64 DS
Presumably due to graphical limitations, Spiny Eggs were absent from the original Super Mario 64, with Lakitu instead throwing fully-formed Spinies. However, they do appear in the DS remake.

New Super Mario Bros.
In New Super Mario Bros., it is revealed that a Spiny can turn back into a Spiny Egg at will when they touch water, and can float on the surface. However, they do not do this underwater in Super Mario Bros. 3 or Super Mario 64.

New Super Mario Bros. Wii
Spiny Eggs reappear in New Super Mario Bros. Wii, acting the same as in previous games.

Super Mario Galaxy 2
In Super Mario Galaxy 2, Yoshi can turn Spinies back to their original form, as well as swallow Spiny Eggs and spit them back out, which can be used as projectiles to hurt enemies or break glass containers.

New Super Mario Bros. 2
In New Super Mario Bros. 2, they again appear. If Mario touches a Gold Ring, Lakitu will instead throw Coins.

New Super Mario Bros. U/New Super Luigi U
Spiny Eggs once again reappear in New Super Mario Bros. U, along with a Piranha Plant-based subspecies.

Super Mario Bros.: Peach-hime Kyushutsu Dai Sakusen
In Super Mario Bros.: Peach-hime Kyushutsu Dai Sakusen, Spiny Eggs appeared twice. The first time was a role as one of the enemies coming out of Mario's TV. The second time was when a Lakitu threw several Spiny Eggs at the trio but it missed then he used rain and a mirror which made them grew into Spinies.

DIC cartoons
Spiny Eggs briefly appear in The Super Mario Bros. Super Show! episode "Mario and the Red Baron Koopa", where they are entirely pink, and act more or less like they do in Super Mario Bros.. Later on, a single, green Spiny Egg is thrown by a Lakitu in The Adventures of Super Mario Bros. 3 episode "Life's Ruff". This Spiny Egg makes a small explosion upon hitting the ground and turning into a normal Spiny.

Nintendo Adventure Books
Some Spiny Eggs, presumably transported to Dark Land by Wendy O. Koopa (who needs them for use in a potion) appear in Koopa Capers. While exploring a Fortress, Luigi finds a room filled with the eggs and some Ptooie, but he manages to evade them while wondering what they are doing in a dank fortress chamber, instead of being outside.

Super Mario RPG: Legend of the Seven Stars
While not Spiny Eggs per se, similar-looking Eggs are seen in Super Mario RPG: Legend of the Seven Stars, where they instead hatch into Spikies, Spikesters, and Oerlikons. The former two are thrown by Lakitus, the latter are knocked down from the ceiling by a Corkpedite.

Paper Mario
In Paper Mario, Spinies could roll back into Spiny Eggs to attack. They appear in Flower Fields. Lakilester also uses Spiny Eggs in the attacks Spiny Flip and Spiny Surge, although they don't hatch.

Paper Mario: The Thousand-Year Door
In Paper Mario: The Thousand-Year Door, Spinies again attack by rolling into Spiny Eggs, and can now roll into Eggs on any turn to make themselves invulnerable. They appear in The Glitz Pit. When Sky-Blue Spinies roll back into a Spiny Egg, they turn into "Sky-Blue Pipes," which are named as such due to mistranslation of the Japanese name, Paipo.

Super Paper Mario
In Super Paper Mario, Spiny Eggs act as they do in Super Mario Bros.. They are found in The Dotwood Tree, The Overthere, and The Flipside Pit of 100 Trials. They do not have a dark version.

Paper Mario: Sticker Star
Spiny Eggs appear only when being thrown by Lakitu in this game, and as such only on the overworld. Lakitu will endlessly throw them, leading to an endless supply of Spinies.

Paper Mario: Color Splash
Spiny Eggs reappear in Paper Mario: Color Splash, acting the same as in Sticker Star.

Mario Party series
In Mario Party Advance, Spiny Eggs appeared as obstacles in the mini-game Dreadmill. In Mario Party 8, they appeared in the mini-games Water Ski Spree, Winner or Dinner and Grabbin' Gold.

Mario & Luigi: Partners in Time
Spiny Eggs also appear in Mario & Luigi: Partners in Time where they are used as projectiles from Shrooba Divers.

Mario & Luigi: Bowser's Inside Story
In Mario & Luigi: Bowser's Inside Story, large golden Spiny Eggs are thrown by Glam Lakitus and Lakitu Kings. They do not hatch.

Mario & Luigi: Dream Team
In Mario & Luigi: Dream Team, Lakitus and Lakitus R attack by throwing Spiny Eggs at the bros. During the battle with Bowser Jr., the bros. can throw Spiny Eggs at him if they take his Junior Clown Car.

Mario Party: Island Tour
Spiny Eggs reappear in Mario Party: Island Tour, Lakitu throws them in the minigame, Pachinko Wizard to eliminate players, some of them appear in the minigame, Deck Hunt, where they reduces the player's coin count upon contact.

Super Mario Maker / Super Mario Maker for Nintendo 3DS
Spiny Eggs reappear in Super Mario Maker and Super Mario Maker for Nintendo 3DS. When a Spiny is placed in the Underwater level style, the Spiny turns back into a Spiny Egg and begins floating in place. If Mario hits a block while a Spiny Egg is above it, it will turn back into a Spiny.

Super Mario World 2: Yoshi's Island
In Super Mario World 2: Yoshi's Island, Spiny Eggs are thrown by Lakitus, Wall Lakitus, and Aqua Lakitus. In this game, they do not hatch, but explode, with the various Lakitus gaining a crosshair to aim, similar to Yoshi with his Eggs. In Yoshi's Story, Lakitu instead throws rocks and Bob-ombs.

Yoshi's Safari
In Yoshi's Safari, Lakitus once again throw Spiny Eggs to attack.

Yoshi's Island DS
In Yoshi's Island DS, Spiny eggs act exactly the same as in the first Yoshi's Island game.

Yoshi's New Island
They reappear in Yoshi's New Island, again acting as they did in Yoshi's Island.

Yoshi's Woolly World / Poochy & Yoshi's Woolly World
In Yoshi's Woolly World and its remake, Spiny Eggs again act as they did in Yoshi's Island.