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Duplicate key items glitch: Difference between revisions
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<!--Some information taken from ChickasaurusGL's TM33 arbitrary code execution video https://www.youtube.com/watch?v=BgCJxChdonc with permission-->
{{PRAMA|infinite-pc-items-trick}}
This '''duplicate Key Items glitch''' is a glitch in {{GSC}}, in which the player swaps two identical key items (obtained via byte shifting from [[????? party overloading]]) in the Key Items pocket to obtain items (such as infinite use Rare Candies) or allow the player to set up an expanded Balls pocket with more than the maximum amount of items.
The reason the player obtains arbitrary items in the Key Items seems to be related to the facts that both: item quantities in the Key Items do not exist, and the game tries to merge the two stacks into one stack with a combined quantity.
Using the expanded Balls pocket, the player is able to use TMs and HMs from the wrong pocket for their own glitchy effects and [[arbitrary code execution]] (e.g. via TM33 in English Crystal, TM15 in English Crystal and TM25 in English Gold and Silver).
These TMs run code from the enemy Trainer's fifth Pokémon's nickname character 3 (TM33) or somewhere in the expanded Balls pocket.
Furthermore, the player can also enable [[glitch Pokédex categories]] (such as glitch Pokédex mode 09 in English Crystal for arbitrary code execution in the expanded Balls pocket) as well.
==Via arbitrary code execution==
This trick requires being able to set up [[arbitrary code execution]] on {{RBY}}. You may use 8F or ws m in Generation I to change the catch rate of Pokémon to value(s) corresponding to key items. (see [[The Big HEX List]] to see which IDs correspond to which key items)
==Via [[bad clone glitch]] and [[????? party overloading]]==
Using tricks from ????? party overloading, the player can manipulate a key item as a held item on a Pokémon. This can be done in practise by using move PkMn w/o mail to obtain a seventh Pokémon, placing a Pokémon in slot 1 with a specific move then performing 1-4 shifts (depending on the position of the move) to shift the move ID into an equivalent held item ID. (see The Big HEX List to see which IDs correspond to which moves and held items)
===Example: Obtaining TM17 in the ball pocket using duplicate bicycles===
This works in any language version on any generation 2 game, the method is based on a translation of a [[https://nakayoshibaddi.hatenadiary.jp/entry/2017/08/15/223932 blogpost from 任意コード]]. When in the ball pocket, TM17 functions as a wrong pocket TM with its effect pointer at $DA47 (middle of the first party pokémon's data).
====Requirements====
Have the following items in the ball pocket:
* Slot 1: any x2
* Slot 2: any xany
* Slot 3 and beyond: empty
Have the following items in the key item pocket:
* All key items you've obtained in your save thus far (withdraw all key items you stored from the PC)
* Bicycle at the bottom of the key item list
Have the following pokémon in the party:
# Bad clone
# Drowzee with Fire Punch in second move slot
# Drowzee with Fire Punch in second move slot
# Unwanted pokémon
# Unwanted pokémon
# Unwanted pokémon
(you can buy the TM for Fire Punch at the Goldenrod Dept. Store)
Have the following pokémon in the box:
* 1 unwanted pokémon
* 1 normal pokémon
====Obtaining duplicate bicycles====
* Step 1: Deposit the bad clone in the daycare and retrieve it. It will now have turned into a glitch pokémon. Arrange your party as follows:
# Glitch pokémon
# Drowzee with Fire Punch in second move slot
# Drowzee with Fire Punch in second move slot
# Unwanted pokémon
# Unwanted pokémon
# Unwanted pokémon</pre>
* Step 2: Using "move pokémon w/o mail", add the stored unwanted pokémon to the top of your party.
* Step 3: Switch the party pokémon in the second slot (the glitch pokémon) with the pokémon in the fifth slot (an unwanted pokémon).
* Step 4: Select "Deposit pokémon" from the PC and deposit the top two pokémon in your hand.
* Step 5: Withdraw the normal pokémon from your box and add it to the party using "Withdraw pokémon".
The party will now contain two Drowzee that will both be holding a bicycle each. Take these held items to add them to the bottom of the Key Item list. '''It is now safe to save.'''
====Obtaining TM17====
* Step 1: Go to the bottom of the key item list. The bottom of the list should consist of three separate bicycles.
* Step 2: Press select on the '''second''' bicycle and swap it with the '''third''' bicycle. The number of bicycles will decrease, the "Cancel" button will change to a "Teru-Sama" item.
* Step 3: Go to the ball pocket and toss 47 of the '''second''' item. The final quantity of the second item is a number ending in "8".
* Step 4: Return to the Key Item pocket, press select on the '''upper''' bicycle and swap it with the bottommost item. This leaves you with a single bicycle, will turn the "Teru-Sama" into a "Paralyz Heal" and change the second item of the Ball pocket into a TM17. '''It is now safe to save.'''
After obtaining TM17 in the Ball pocket you can use ACE to remove the glitchmon from your party and change the "Paralyz Heal" in your Key Items pocket back into a cancel. Alternatively, obtain another key item to restore the cancel. The glitchmon can temporarily be stored at the daycare.
==Infinite items examples==
Example 1:
If we have the following items:
Lost Item
Lost Item
Card Key
Basement Key
Cancel
Then swapping the first Lost Item with the second Lost Item will make us lose the original second Lost Item and Card Key but the second Lost Item will turn into a Master Ball with quantity 133 (Basement Key's index number). The Master Ball can be used infinitely because it is in the wrong pocket.
If we have the following items:
Lost Item (index no. 130)
Lost Item (index no. 130)
Card Key (index no. 127)
Basement Key (index no. 133)
Cancel (index no. 255)
If we swap the first Lost Item with the second, we lose the original second Lost Item and the Card Key, but the second Lost Item will turn into a Master Ball with quantity 133 (Basement Key's index number). The reason why the second item turns into a Master Ball in this example is because the Card Key is index number 127 (7F) and the Lost Item is index number 130 (82). Adding these together gives 257, but since items are defined by one byte, this becomes 257 modulo 256 or 1, which is Master Ball's index number.
Therefore we get:
Lost Item (index no. 130)
Master Ball (index no. 257 == 1) x133
CANCEL (index no. 255)
Example 2:
If the sum of the first Key Item's index number and the item below the second Key Item is greater than 100, then the third item is not lost, but becomes a BLK Apricorn (index no. 99). The second item identifier becomes equal to that of the sum of the first Key Item index number and the original third item minus 99. Its quantity is derived from the new third item identifier.
For example, consider the following Key Items pack:
Lost Item (index no. 130)
Lost Item (index no. 130)
Master Ball (index no. 1) x7
Bicycle (index no. 7)
Cancel
If we swap the first Key Item with the second this gives us:
Lost Item (index no. 130)
Rare Candy (index no. 32 [130+1-99] )
BLK Apricorn (index no. 99)
Bicycle (index no.7)
CANCEL (index no. 255)
===Expanded items pack===
If you want to set up the expanded Balls pocket, change the catch rate of two Pokémon to 128 and 67 each. When traded to a Generation II game they will be holding Machine Parts and Secretpotions.
# On the game with two SecretPotions and two Machine Parts
# Put both Machine Parts in the last two slots of the Key Items pocket
Line 20 ⟶ 147:
# Put both SecretPotions in the last two slots of the Key Items pocket
# Swap these, and all bytes up to the Cancel in the Balls pocket will be shifted upwards
==Expanded Balls pocket==
Using specific duplicate key items, it is possible to enable the expanded balls pocket, which can later be used for memory corruption by swapping items in the pocket or arbitrary code execution via [[glitch item|TMs/HMs outside of the correct pocket]] or [[glitch Pokédex categories]].
First the key items pocket must be filled with 25 items including two Machine Parts and two Secretpotions:
Then..
# Put both Machine Parts in the last two slots of the Key Items pocket
# Swap both items to create Iron x99 and Blk Apricorn x10
# Put both SecretPotions in the last two slots of the Key Items pocket
# Swap these, and all bytes up to the Cancel in the Balls pocket will be shifted upwards, with the ID of the first item becoming the number of Balls.
Note that this is not the only way to access the expanded balls pocket. The Pokémon Speedruns wiki [http://archive.is/IEmNE details a different method] involving two Itemfinders.
==YouTube video==
{{YouTube|FZrFMi6B0jQ|ChickasaurusGL}}
[[Category:Generation I glitches]]
[[Category:Generation II glitches]]
[[Category:Glitches between two generations]]
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