It is considered a special evolution of Nincada, appearing only when Nincada evolves into Ninjask at level 20, as long as there is an extra space in the player's party and an extra Poké Ball in the player's bag. An extra Poké Ball is not necessary to obtain Shedinja in Generation III.
Shedinja is a Pokémon based on a cicada's shed exoskeleton. Most of its body is light brown, but the abdomen is gray. It has four protrusions on its underside instead of legs; the top pair is brown, while the lower is gray. There are round protrusions on the side of its head with narrow slits for eyes. Two lines encircle its abdomen and a white halo floats above its head. On its back is a pair of tattered wings divided into three wingtips. A hole between its wings reveals that its body completely hollow and dark, as it possesses no internal organs. It is said that looking into this empty space will steal one's spirit. Its shell is very hard, which gives it strong defense but renders it incapable of movement. It does not breathe and floats without moving its wings. It lives in forests.
Shedinja first appeared in Can I Ninjask You a Question?, when Aqua Admin Amber, having been deprived of his Pokémon after being abandoned by Archie, borrows a Nincada from his comrade Shelly, which then immediately evolves into a Ninjask, putting Wattson in quite a pinch with the incredible speed it gained by the minute. Although the old Gym Leader eventually managed to defeat it, a Shedinja formed from the shell Ninjask shed and attacked him from behind, sending him sinking into the ocean.
In Sneaky Like Shedinja, Greta used Shedinja to exploit its Wonder Guard Ability, as well as the fact that it has one base HP, requiring no items to resuscitate itself.
Shedinja's hard body doesn't move - not even a twitch. In fact, its body appears to be merely a hollow shell. It is believed that this Pokémon will steal the spirit of anyone peering into its hollow body from its back.
Shedinja’s hard body doesn’t move—not even a twitch. In fact, its body appears to be merely a hollow shell. It is believed that this Pokémon will steal the spirit of anyone peering into its hollow body from its back.
From Generation IV onwards, a basic Poké Ball (a requirement for evolution) is removed from the bag upon evolution to produce a Shedinja. In Generation III, Shedinja instead copied the ball Nincada was in; this is the only legitimate way to get a Shedinja in a non-standard Poké Ball.
Shedinja inherits the same game of origin, personality value, IVs, EVs, OT, Trainer ID number and Secret ID number, and met location as the Nincada that shed it. It also inherits the Pokérus if the Nincada had it. Among other things, due to keeping the same game of origin, personality value, and Trainer and Secret ID numbers, Shedinja will be Shiny if and only if the Nincada was Shiny.
The Shedinja shed from a Nincada has no nickname, and the player is not given an opportunity to nickname it. The only way to give Shedinja a nickname is for the Nincada's original Trainer to take it to a Name Rater.
Shedinja's Wonder Guard Ability renders it immune to 13 of 18 attack types, the most of any Pokémon; four of these immunities (to Ice, Bug, Steel, and Fairy) are entirely unique to Shedinja. This also gives it a few further distinctions:
If Soak is used to make Shedinja a Water type, it will have immunities to 16 of 18 attack types.
Prior to Generation V, if Nincada learns a move upon evolving into Ninjask, Shedinja will also know this move. This means that Shedinja can learn any of Ninjask's level up moves starting at level 20, but can only simultaneously have multiple of them if they are learned at the same level. From Generation V onward, Shedinja starts with the moves Nincada knew prior to evolution.
In Pokémon Super Mystery Dungeon, wild Shedinja will spawn on any tile where a wild Nincada was defeated after several turns have passed. They move once every two turns and do not attack. Additionally, other wild Pokémon will try to attack the wild Shedinja if they are nearby, allowing them to evolve without defeating the player or their allies if they succeed in causing it to faint.
1 HP trivia
Shedinja has many unique characteristics derived from the fact that it has only 1 HP:
Shedinja is the only Pokémon to have a stat not calculated by the standard formula; if it were, Shedinja would have at least 11 HP even at level 1.
Shedinja is the only Pokémon that cannot gain any additional HP EVs.
Having only 1 HP, Shedinja's Defense and Special Defense stats normally have no practical purpose in battle. However, if Shedinja receives a substitute through Baton Pass, its Defense and Special Defense are factored into damage the substitute takes. Shedinja's Defense and Special Defense stats also become relevant if a Pokémon uses Transform on it or if Shedinja uses Power Trick (via Mimic).
From Generation IV onward, Shedinja is the only Pokémon that can knock itself out from full health with the recoil damage from Struggle.
It is based on the shed husk that cicadas leave behind when they finish their metamorphosis into adults. Concerning its species' ninja theme, it also appears to be a reference to the fabled ninjutsu technique 空蝉 utsusemi, where a ninja uses a dummy or replica of itself to evade and escape from threats, and where its namesake also alludes to the cast off shed husk of a cicada. It may also be based on a guardian angel, due to the halo-like object floating above its head. Its Ability Wonder Guard probably alludes to this.
Shedinja is a combination of shed (to cast off skin or exoskeleton) and ninja.
Nukenin is a pun on 抜け忍 nukenin, a term for ninja who have abandoned their clan and lord. It also combines 抜け殻 nukegara (casting off skin) and ninja.