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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 series
Spiny Eggs debuted in the original Super Mario Bros., and Super Mario Bros. 3 introduced a green Spiny Egg, which never hatched, but only rolled around on the ground. In New Super Mario Bros., it is revealed that a Spiny will turn back into a Spiny Egg at will when they touch water, and can float on the surface. 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.
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.
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.
Paper Mario: The Thousand-Year Door
Mario Party series
Mario & Luigi: Partners in Time
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.
Names in other languages