Base structure Pokédex marker byte

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The base structure Pokédex marker byte is a byte in Pokémon Red, Blue, and Yellow and Pokémon Gold, Silver and Crystal found in the ROM at the beginning of a Pokémon's "base stats data structure" (shared attributes for Pokémon of the same family) that is intended to be equal to the Pokémon's Pokédex number.

The Pokédex marker byte may serve as minor detail about a glitch Pokémon's family as it may not be equal to the glitch Pokémon's Pokédex number.

This byte according to Stag019 is supposed to be the same as the Pokémon's Pokédex number, but for many glitch Pokémon it is different. 'M (00) and MissingNo. in Red/Blue are exceptions. They have a Pokédex marker byte of 0x00, which is the same as their Pokédex number.


The location of a glitch Pokémon family's base stats data can be found using the following:

0x0383DE + (PkmnNo. − 1) × 0x1C


Presumably hybrid glitch Pokémon will have the same Pokédex marker byte as their Pokédex number, due to having their base data derived from real Pokémon.

In Generation II, it is used to determine the Pokédex entry bank.[1]

List of families and Pokédex marker bytes

In Yellow

Pokémon's Internal ID ROM offset Marker byte
000 39FC2 0x28
176 39702 0xF9
159 39526 0x3C
195 39916 0x62
202 399DA 0x81
203 399F6 0x87
205 39A2E 0x86
207 39A66 0x92
215 39B46 0xFE
229 39CCE 0x01
230 39CEA 0x5A
234 39D5A 0x05
245 39E8E 0x00
250 39F1A 0x00
254 39F8A 0x14
255 39FA6 0x1E


In Red/Blue

Pokémon's Internal ID ROM offset Pokédex Marker
000 39FC2 0x00
174 396CA 0xCB
175 396E6 0xC3
205 39A2E 0x91
209 39A9E 0x8F
211 39AD6 0xF7
213 39B0E 0x82
224 39C42 0x05
234 39D5A 0x60
240 39E02 0x00
245 39E8E 0x00
250 39F1A 0x19
254 39F8A 0x6A
255 39FA6 0x37

References