Pokémon Red and Blue: Difference between revisions
→Obtaining
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Similar to Pokémon species, in Generation I games the ID of an item can take any of its 256 values, while valid item IDs range either from 1 (Master Ball) to 83 (Max Elixer), or from 196 (HM01) to 250 (TM50). Furthermore, some IDs in the "valid" range do not correspond to items intended to appear in the game. However, most of them have distinct names and/or effects, and some of them are designed to play a role in gameplay:
* [[ItemDex/RGBY:007|?????]] (ID 7) is usually known as the "Surfboard", because it acts identically to the move [[bp:Surf|Surf]] outside of battle. In fact, the field move Surf internally "uses" this item (i.e. calls the "item use" subroutine with this item's ID), just like the field move [[bp:Dig|Dig]] does with [[bp:Escape Rope|Escape Rope]].
* [[
* [[
* Items with ID 21–28 have the names of the Gym Badges, from "BoulderBadge" to "EarthBadge". Those names are used to display a list of all badges when the player talks to Cerulean City's badge describer.
** Furthermore, the first two of those, [[
** The rest of those items are designed to be unusable anywhere, just like some valid items that are supposed to be checked rather than directly used from the menu (e.g. the [[bp:Helix Fossil|Helix Fossil]]), or exist just to be sold (i.e. the [[bp:Nugget|Nugget]]).
* [[ItemDex/RGBY:044|?????]] (ID 44) is an unusable glitch item.
* [[
* [[ItemDex/RGBY:059|Coin]] (ID 59) is an unusable glitch item.
In addition, all items with IDs greater or equal to 196 are considered HMs or TMs, and are handled in a special way. This means that the items with ID 251–255 are named TM51–TM55, and act as TMs. They actually teach exactly the same moves as HM01–HM05, to exactly the same Pokémon, because even though the valid HM items have IDs before the TM items, for all other purposes, the HM moves come after the TM moves in the game's internal data. However, since TM51–TM55 are considered as TMs rather than HMs, they are not key items (i.e. their quantities are displayed in the inventory, and they can be tossed or sold), and are consumed when used. ([[
Apart from the above glitch items, other glitch items have IDs outside of the valid range, i.e. either 0 or 84–195. They take data from mostly unrelated memory regions, as detailed below.
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=== Obtaining ===
In most cases, glitch items are obtained from the [[expanded item pack]]. Putting the game into certain states will cause certain items to appear in the expanded item pack, which can either be used from there or switched into valid item slots to preserve them, although care must be taken because modifying the expanded item pack also changes the game state. The [[Celadon looping map trick]] can help the player obtain any item, except [[
Other methods to obtain glitch items include item mutation through certain [[glitch Pokédex flags]], as well as arbitrary code execution, which, once set up, may again be the most convenient method to manipulate the player's inventory, including item types and item quantities.
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