From Bulbapedia, the community-driven Pokémon encyclopedia.
In each Pokémon game of Generation I, all Pokémon have an unseen index number used to identify them in the game's ROM. Unlike later generations, the Pokémon are far from being in order by their National Pokédex numbers, and most evolution families are extremely fragmented. In addition, the glitch Pokémon Missingno. permeates the list; all other glitch Pokémon are either indexed 0x00 (dec 000) or after Victreebel. Since Rhydon is index number 0x01 (dec 001), many glitch Pokémon will become it upon capture, due to the Rhydon glitch.
When connected to a Generation II game, many of the glitch Pokémon will appear to the other side to be a Generation II Pokémon and are occasionally tradable. In the list below, the name of the Generation II Pokémon in parentheses after the glitch Pokémon's name is the equivalent Pokémon in the Generation II games. The conversion of Generation I glitch Pokémon index numbers to Generation II index numbers simply is Johto Pokémon in National Pokédex order; starting from 0xBF (dec 191)—the index after the last valid Pokémon in Generation I—and ranging to 0xFA (dec 250), then continuing by filling the indices that correspond to Missingno.; only Ho-Oh and Celebi are misplaced.
List of Pokémon by index number
Please note that the Ghost, Kabutops Fossil and Aerodactyl Fossil Missingno. are not of type Bird/Normal and use the same type as the last Pokémon in memory.
Garbage data (glitch Pokémon)
- In an interview with Shigeki Morimoto, he confirmed that there were originally going to be 190 Pokémon in Generation I. This would mean that the 39 Missingno. are formatted Pokémon.