From Bulbapedia, the community-driven Pokémon encyclopedia.
This is a list of Pokémon by the items they may be holding when encountered in the wild in Generation II, or when obtained in Generation I and traded to Generation II.
Generation I held items
In the Generation I games, there are no held items; however, Pokémon are holding an item by default when traded to a Generation II game. These items are determined by a value in the Pokémon data structure that has no effect in Generation I, and is set to that species's catch rate upon obtaining it. Therefore, a given Pokémon's catch rate translates into the item it will be holding by default when traded to Generation II.
In Pokémon Yellow, four Pokémon will have different held items than their Red/Blue counterparts when traded to Generation II. The starter Pikachu's held item value is specially set to 163 (as opposed to Pikachu's catch rate of 190) when it is obtained, which causes it to hold a Light Ball when traded over. A wild Kadabra's held item value is set to 96 upon capture (as opposed to 100), which gives it a TwistedSpoon when traded over. Finally, Dragonair and Dragonite's actual catch rates are different, having been changed to 27 and 9 respectively in Yellow only. This means Dragonair caught in Yellow will have a held item value of 27 and thus hold a Protein when traded over, and a wild Dragonite caught in Yellow would have a held item value of 9 and therefore hold an Antidote. Wild Dragonite cannot normally be found in Yellow, however.
Some catch rate values do not directly correlate into an item when traded. Instead, they correspond to Teru-sama, other glitch items, or Key Items. To compensate for this, the given value is converted into an entirely different number when traded to Generation II.
Items held in Generation II (including holding no item) will be conserved when traded to Generation I and will not be changed back to the Generation I item.
Because items are only set when a Pokémon is caught, evolving it does not change the held item. The "Gen I" header below contains data for held items the Pokémon would possess if it were caught in the wild without any evolution involved.
Generation II held items
For wild Pokémon in Generation II games, the chance of holding a rare item is 5/256, based on a randomly generated byte upon encounter. Several Pokémon may hold a second item with odds of 59/256. If the first and second item are the same, these odds add together to make a 1/4 chance of holding that item. Several Pokémon that cannot be found in the wild have a chance of holding an item, but these cannot be obtained without cheating. The Ho-Oh found in Tin Tower has a flag set so that it will always be holding Sacred Ash. This also applies to the Snorlax in Vermilion City holding Leftovers. However, any other Ho-Oh or Snorlax encountered (through cheating) have the same odds as all other Pokémon.
Held item table