Bad Egg - Bulbapedia, the community-driven Pokmon encyclopedia

October 2024 · 30 minute read
A Bad Egg in the party in Generation III

A Bad Egg (Japanese: ダメタマゴ Bad Egg) is an error handler in the core and side series Pokémon games and Pokémon HOME for Pokémon with invalid data, most often because of a checksum mismatch. Bad Eggs were introduced in Generation III under the name "Bad EGG", and have appeared in subsequent games under the name "Bad Egg" or "Egg". While they have the same appearance as and share some properties with a regular Pokémon Egg, Bad Eggs behave differently in several ways.

The term "Bad Egg" is sometimes also used for glitch Pokémon species with the name "Egg" or "Bad Egg" that can appear from Generation IV onward, or the error handlers for Pokémon species and forms that are not coded into Pokémon Brilliant Diamond and Shining Pearl. However, unlike an actual Bad Egg that appears due to a failed checksum, these Pokémon can battle and be released like any other hatched Pokémon. Bad Eggs should also not be confused with regular Eggs in games where Eggs do not normally appear, and regular Eggs modified to display "Bad Egg" as a nickname.

Causes

A Bad Egg in the Boxes in Pokémon HOME

All core series Pokémon games from Generation III onward, Pokémon Box Ruby & Sapphire, and My Pokémon Ranch, calculate a checksum over most of a Pokémon's data before storing it in an encrypted form. This checksum is stored in an unencrypted portion of the Pokémon data structure. When the games load a Pokémon's data, they decrypt it and recalculate the checksum over the decrypted data. This checksum is compared to the stored value, and if they do not match, the game sets the Bad Egg flag located in an unencrypted portion of the Pokémon data structure. Other parts of the game check this value and treat the Pokémon as a Bad Egg as a result. The checksum can fail to match due to data corruption (such as through glitches, communication errors, failing flash memory, or bit flips) or external modifications that alter a Pokémon's data without recalculating the checksum (such as through exploits, cheating, or third-party tools).

In Pokémon Black 2 and White 2, Pokémon with an index number greater than 649 (such as Pokéstar Studios opponents) are marked as Bad Eggs if put in the player's party. In Pokémon: Let's Go, Pikachu!, Let's Go, Eevee!, and Legends: Arceus, Pokémon with species, forms, or moves not coded into the game are marked as Bad Eggs. In Pokémon HOME, Pokémon flagged by HOME's cheat detection are marked as Bad Eggs.

In Pokémon Colosseum, XD, and Battle Revolution, checksums are not validated for any Pokémon stored on the game's save file, as Pokémon data is not encrypted by the game. However, they do display Pokémon with the Bad Egg flag in the Game Boy Advance/Nintendo DS games as Bad Eggs. Pokémon Colosseum and XD do not store a Pokémon's checksum at all, and will only calculate a checksum for a Pokémon when it is traded to the GBA games. Pokémon Battle Revolution additionally sets the Bad Egg flag on its copies of Pokémon with more than 510 effort values when they are copied from the handheld Generation IV games.

Appearance

Main article: Pokémon Egg → Appearance

Bad Eggs use the same sprites and models as regular Eggs in all games in which they appear, with the exception of those whose underlying Pokémon species have index number 0 in Generations III and IV:

Properties

In Generations III, IV, and V, Bad Eggs retain and display some properties of the underlying Pokémon. Because of this, if the underlying Pokémon's data would cause the game to freeze or crash (such as displaying invalid markings in Generation III), it may still do so even if the Pokémon has been marked as a Bad Egg. A Bad Egg's markings are displayed and can be modified like any normal Pokémon or Egg.

Starting in Generation VI, the game does not read or write to the underlying Pokémon's encrypted data, and treats it as though all of its data (including its held item and Poké Ball) was zeroed out. As long as the invalid data is detectable by the checksum, this can prevent freezes or crashes that would otherwise occur if the Pokémon data were read normally by the game. The Poké Ball with index 0 displays as a regular Poké Ball in the Nintendo 3DS games, as a question mark in Sword, Shield, Brilliant Diamond, and Shining Pearl, and as a Strange Ball in Legends: Arceus, Scarlet, and Violet. If the player attempts to set any of a Bad Egg's markings, the changes will not be saved.

Bad Eggs ignore the underlying Pokémon's species name or nickname, and display their name as some variant of "Bad Egg" or "Egg" in the language of the game.

In Generation III, the Bad Egg flag is stored unencrypted in the same byte as the has species flag and one of the Egg flags. In Generations IV and V, the Bad Egg flag is stored unencrypted along with a Pokémon's personality value and checksum. Starting in Generation VI, the Bad Egg flag is stored unencrypted along with a Pokémon's encryption constant and checksum. In Generation III only, a Pokémon becoming a Bad Egg sets the Bad Egg flag and both Egg flags in the Pokémon's data structure, unlike in later games.

Behavior

Attempting to release a Bad Egg in Diamond and Pearl Attempting to shift a Bad Egg into battle in HeartGold and SoulSilver

Bad Eggs are generally treated identically to Eggs in most aspects of the game: they are unable to battle, cannot be released, and cannot be left at the Day Care or Nursery. Except in Pokémon Ruby and Sapphire, they cannot hatch and cannot be traded, unlike regular Eggs. Because of this, they effectively take up a permanent slot in the player's party or Boxes until the player starts a new game.

Party

In the party screen, a Bad Egg is displayed in the same way as a regular Egg: it uses the same menu sprite as one, and its HP, level, and gender are not shown. Likewise, a held item cannot be given to or taken from a Bad Egg in the party screen, and any field moves the underlying Pokémon knows are not shown.

Summary

A Bad Egg's summary screen uses the same layout as a regular Egg.

In Pokémon Ruby and Sapphire, the messages displayed on the summary screen depend on the underlying Pokémon's remaining Egg cycles (or friendship interpreted as such) and met location like a normal Egg; in Pokémon FireRed, LeafGreen, and Emerald, the regular messages are overridden with a state of "It looks like this EGG will take a long time to hatch." and a Trainer Memo of "An odd POKéMON EGG found by the DAY CARE couple." In Pokémon Ruby, Sapphire, and Emerald, the underlying Pokémon's Poké Ball and status condition (including Pokérus and fainted) are displayed normally; in Pokémon FireRed and LeafGreen, the Bad Egg's Poké Ball is always displayed as a regular Poké Ball and any status condition is hidden. Any markings are displayed normally.

In Pokémon Box Ruby & Sapphire, the underlying Pokémon's Poké Ball, Pokérus status, and markings are displayed.

In Generations IV and V, the messages displayed on the summary screen depend on the underlying Pokémon's remaining Egg cycles (or friendship interpreted as such), Original Trainer, met date, met location, and fateful encounter status. The underlying Pokémon's Poké Ball, held item, status condition (including Pokérus and fainted), markings, and Shiny Leaves are displayed normally. Note that if the Pokémon has no met data as an Egg and the player is the underlying Pokémon's Original Trainer, it will be displayed as having been received from the location header with index number 0 ("Mystery Zone" in Generation IV or "－－－－－－－－－－" in Generation V) on 0/0/2000 (the zeroth month is displayed as "Jan." in Western-language Generation IV games). In Generation V, navigating directly between summaries of party Pokémon will skip Bad Eggs whose underlying Pokémon species is ―――――.

In the Nintendo 3DS games and Pokémon Sword and Shield, a Bad Egg's summary screen will always display it as being obtained from the Mystery Zone on 0/0/2000 (in the Nintendo 3DS games) or 00/00/2000 (in Sword and Shield) and a "The Egg Watch" message of "Sounds can be heard coming from inside! This Egg will hatch soon!". In Pokémon Brilliant Diamond and Shining Pearl, the Trainer Memo of a Bad Egg cannot be viewed, unlike a regular Egg.

In Pokémon Scarlet and Violet, a Bad Egg's summary screen always displays a "The Egg Watch" message of "It looks as though this Egg will take a long time yet to hatch.", with its met date and met location hidden, unlike a regular Egg. In version 1.0.0 only, a Bad Egg's summary screen will display its language of origin as Japanese.

In Pokémon: Let's Go, Pikachu!, Let's Go, Eevee!, Legends: Arceus, Colosseum, XD, and Battle Revolution, the summary screen of Bad Eggs and Eggs cannot be viewed.

Boxes

A Bad Egg in Storage in Battle Revolution

In the Pokémon Storage System, Bad Eggs are generally treated identically to Eggs. As such, most information about the Pokémon is not displayed.

If the player attempts to release a Bad Egg, a message telling the player that they cannot release an Egg will be displayed:

Mail and Ball Capsules can prevent a Bad Egg from being deposited into the PC:

Depending on the game, a Bad Egg's held item can be seen, taken, or swapped through the PC:

In Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!, a Bad Egg is displayed in the Pokémon Box as a Pokémon at level 0 with 0 CP, whose nickname is the number of Pokémon in the Pokémon Box (regular Eggs are displayed as healthy, with the name "Egg" and the level and CP of the Pokémon inside). Interacting with a Bad Egg or Egg will not bring up the context menu, so they cannot be added to the party or sent to the professor.

In Pokémon Legends: Arceus, Bad Eggs are displayed in the Pastures as fainted, level 0 Eggs when in the player's party, whose Original Partner is displayed as whichever valid Pokémon's Original Partner was displayed last, or a blank string otherwise (regular Eggs are displayed as healthy, with the Poké Ball, level, and origin mark of the Pokémon inside).

In Pokémon Battle Revolution, the Storage displays all Bad Eggs in regular Poké Balls with no held item, regardless of the underlying Pokémon's data.

With a species value of 0

A Bad Egg with a species value of 0 selected in the PC in Emerald

Bad Eggs whose underlying Pokémon species have an index number of 0 behave differently from other Bad Eggs in Generations III, IV, and V:

Trading

050Diglett.pngThis section is incomplete.
Please feel free to edit this section to add missing information and complete it.
Reason: In My Pokémon Ranch, does Hayley accept a Bad Egg in exchange for Mew?
Attempting to take a Bad Egg into the Union Room in Black 2 and White 2

Bad Eggs can only be freely traded from copies of Pokémon Ruby and Sapphire. If a Bad Egg is traded to Pokémon FireRed, LeafGreen, and Emerald, it cannot be traded back after the player leaves the Trade Center.

In certain games, having a Bad Egg in the party prevents the player from accessing certain multiplayer functionality:

Attempting to trade a Bad Egg to XD

In certain games, Bad Eggs are specifically blocked from being traded in a Link Trade:

Although Jasmine and Yancy/Curtis will accept any Pokémon from the player for their traded Pokémon, they will not accept Eggs or Bad Eggs.

Storage

Attempting to deposit a Bad Egg in Box Ruby & Sapphire

Bad Eggs can be deposited into and withdrawn from the Japanese version of Pokémon Box Ruby & Sapphire. Attempting to deposit or withdraw a Bad Egg into or from Western versions of Pokémon Box Ruby & Sapphire will cause the message "A Bad EGG can't be transferred." to be displayed.

Bad Eggs can be deposited in My Pokémon Ranch.[1]

Eggs and Bad Eggs cannot be deposited into Pokémon Bank or Pokémon HOME. Attempting to deposit one into Pokémon Bank will display the message "You cannot deposit an Egg.", while attempting to deposit one into Pokémon HOME will display the message "You can't leave a Pokémon Egg in Pokémon HOME!"

Bad Eggs in Pokémon HOME cannot be released, traded, or moved out of Pokémon HOME. Attempting to release one will display the message "You can't release an Egg!", and attempting to withdraw one will display the message "You can't take that Egg out of Pokémon HOME!". In version 2.0.0, a bug caused an error with error code 10015 if the player attempted to save any changes after entering the Boxes menu of Pokémon HOME while connected to a game that had a Bad Egg in any Box slot.[2]

Eggs and Bad Eggs cannot be transferred between generations:

Eggs and Bad Eggs cannot be sent to the Pokéwalker, as they are grayed out and cannot be selected. Eggs and Bad Eggs cannot be tucked in for the Pokémon Dream World, as they are grayed out during Game Sync and attempting to select one will display the message "Eggs cannot be selected!".

Hatching

In Pokémon Ruby and Sapphire only, Bad Eggs have their Egg cycle counter decrease and can hatch in the same way as regular Eggs. However, because they are treated as if they have a species index of 412, they will attempt to hatch into -, which cause the games to softlock on a black screen after the "Oh?" message and before the hatching animation begins.

In all other games, Bad Eggs do not have their Egg cycle counter decrease and cannot hatch. In Generation V, a Bad Egg with an Egg cycle counter of 0 will display "Oh?" with every step taken, but will not hatch.

Glitches

The Battle Tower cloning glitch in Pokémon Emerald can be used to delete Bad Eggs by depositing them into the PC during the cloning process.

If the trapping Ability flee glitch in Pokémon Platinum is triggered when the wild Pokémon on the right side has been knocked out, it will display that "The wild Bad Egg prevents escape with <Ability>!".

Game data

Game locations

Generation III
Generation IV
Generation V
Generation VI
Generation VII
Generation VIII
Generation IX

In events

Poké Portal News

This corrupt event was only accessible if a player running Scarlet and Violet v1.1.0 updated their Poké Portal News data between ~15:30 UTC (following the February 27, 2023 Pokémon Presents livestream reveal of Walking Wake and Iron Leaves) and an unknown number of hours later, when the game ceased to allow players running v1.1.0 to connect online.

Bad Eggs without the Egg flag set

Bad Eggs with (slots 1–3) and without (slots 4–6) the Egg flag set A Bad Egg chosen to migrate as a Burmy

In Generation III, Pokémon that have the Bad Egg flag set, but not the Egg flag, behave differently from other Bad Eggs. While code that explicitly checks the Bad Egg flag will still treat it as a Bad Egg and code that checks the species value or species-or-Egg value will still treat it as an Egg, code that checks if one of the Egg flags are set will not. These can be obtained through arbitrary code execution or cheating.

Their name and sprite is still that of a Bad Egg, unless the underlying Pokémon species is ?????????? (index number 0), in which case they display no menu sprite and use ??????????'s sprite when their summary is viewed. They are treated as if they have a species index of 412 (the same as -), meaning they have base stats of 33/2/45/8/73/14 (HP/Atk/Def/Spe/SpA/SpD), are Tough/Cute-type (which are not weak, immune, or resistant to any type), have a catch rate of 77, have a base experience yield of 30, have EV yields of 3/3/0/1/2/3 (HP/Atk/Def/Spe/SpA/SpD), have a wild held item of ???????? with index number 0x284B (50%) or 0x32E6 (5%), a gender threshold of 74 (71.09% male and 28.91% female), take 64 cycles to hatch, have 235 base friendship, in the experience group with index number 78, in the Egg Groups with index numbers 76 and 92, have the Ability with index number 255, have a Safari Zone escape rate of 33, and have a color of yellow.

Unlike other Bad Eggs, they can battle (though they must be switched in, even if they are the first Pokémon in the party). On the party screen, their HP, level, and gender are shown, a held item can be given to or taken from it, and any field moves it knows are shown. Their summary screen is the same as - in Pokémon Ruby and Sapphire, and the same as other Bad Eggs in Pokémon FireRed, LeafGreen, and Emerald. In the Pokémon Storage System, they are treated like a regular Pokémon (and can be released) in Pokémon Ruby and Sapphire, and the same as other Bad Eggs in Pokémon FireRed, LeafGreen, and Emerald. In Pokémon Ruby and Sapphire, their Egg cycle count does not decrease by walking and they will not hatch, since they do not have the Egg flag. Their friendship does not increase by walking, as they use the species index of an Egg. If left in the Day Care with a Ditto, the resulting Egg will hatch into -.

Bad Eggs without the Egg flag set and - appear as Burmy in the migration interface in Japanese versions of Pokémon Diamond and Pearl, and as a question mark in Western and Korean versions of Pokémon Diamond and Pearl and all versions of Pokémon Platinum, HeartGold, and SoulSilver. A Bad Egg without the Egg flag set whose underlying Pokémon species has an index number of 0 can be migrated to the Japanese versions of Pokémon Diamond and Pearl, where it becomes a Burmy with an empty string as a nickname.[3] Unlike -, Eggs, and other Bad Eggs, it bypasses the "An Egg cannot migrate!" check due to the species-or-Egg value returning 0 (instead of 412); unlike other Pokémon and Eggs with a species index of 0, it bypasses the "This Pokémon is not permitted to migrate." check due to having the Bad Egg flag set, which causes the species value to return 412 (instead of 0), which is within the valid range of index numbers (between 1 and 412 inclusive). This is fixed in Western and Korean versions of Pokémon Diamond and Pearl and all versions of Pokémon Platinum, HeartGold, and SoulSilver, where only Pokémon with index numbers between 1 and 251 inclusive or between 277 and 411 inclusive can be migrated.

As a glitch Pokémon

A glitch Bad Egg's summary in Diamond, Pearl, and Platinum

From Pokémon Diamond and Pearl to Pokémon Sword and Shield, both "Egg" and "Bad Egg" ("Egg" in Pokémon Black and White and starting in Generation VI) are used as the names of glitch Pokémon species that occupy the first two index numbers after the last valid Pokémon index number. These are equivalent to the glitch Egg from Generation II and - from Generation III. If they do not have the flag set that causes them to be treated as an Egg or Bad Egg, they will behave more like regular Pokémon. The data of these glitch Pokémon depends on the game.

In the Nintendo DS games, they are treated specially compared to other glitch Pokémon with index numbers greater than the last valid Pokémon index number.

A glitch Egg's summary in Sun and Moon

In the Nintendo 3DS and Nintendo Switch games, invalid Pokémon species (including "Egg"/"Egg") use the same stats as the entry with index number 0 in the Pokémon data structure, which has the same values as in Generation V. They learn no moves, so they can only use Struggle. Starting in Pokémon Sword and Shield, this also applies to invalid forms. Because they are in the Egg Group with index number 0 rather than No Eggs Discovered (which has index number 15), they can breed with Ditto.

In Pokémon: Let's Go, Pikachu!, Let's Go, Eevee!, and Legends: Arceus, these species do not appear, as invalid Pokémon species are marked as Bad Eggs.

Similar glitch Pokémon

A glitched empty slot

In Pokémon Brilliant Diamond and Shining Pearl, the menu sprite of an Egg is used for Pokémon with invalid species or forms. In battle, they appear with the model of a female Shiny Pikachu and use Pikachu's cry. Attempting to view them on the party screen in the menu, view them in the Boxes, or attempting to check their summary when viewing the party in battle causes the game to crash. These could be obtained in several ways using the menu storage glitch prior to version 1.1.3:

In other languages

Notes

  • ↑ These lines are mistranslated due to the English lines being carried over from Pokémon Platinum, HeartGold, and SoulSilver (where a player could only trade the Pokémon in their party), despite the Japanese lines having been changed from the corresponding lines in those games. A more accurate translation would be "The Pokémon that you offered cannot be traded." and "The Pokémon that the other Trainer offered cannot be traded."
  • ↑ This line is misleading due to the same line being used for both situations when only Bad Eggs cannot be traded (in Link Trades) and when any Egg cannot be traded (in the GTS and Wonder Trade). In later games, "You can't offer that Egg in trade." is used for the former situation and "You can't offer an Egg in trade." is used for the latter situation.

    • References

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