Viewing the summary of specific ????? in specific versions allows the player to cause map corruption, due to the Pokémon having a type with a name that is very long.
????? are obtainable through the bad clone glitch or Coin Case arbitrary code execution. If the bad clone glitch is used the player should initially receive a hex:00 ?????.
It can be converted into a hex:FF ????? after being taken into the Day Care and out again if moved to the top of the party with a party of six Pokémon and the "move PkMn w/o Mail" option is used to move a seventh Pokémon to the top of the party, which moves the hex:00/hex:FF ????? hybrid to the second slot of the party.
????? (FF) - Pokémon Crystal JP.
????? (00) - Pokémon Crystal EN (type hex:50).
????? (00) - Pokémon Crystal ES — freezes believed to be less frequent than on the English version.
Hex:FF ????? items and TM/HM pocket corruption in Japanese Crystal
The spot to secure a warp to the Bug-Catching Contest with the items and TM/HM pocket corrupted.
If the player views the summary of an hex:FF ????? at the specific spot in a Japanese version of Crystal, they may receive an announcement that the Bug-Catching Contest has ended (even if it was never started) and be warped to the results room.
Many items in the player's bag may become corrupted and the player may receive an expanded items pocket every TM/HM in the TM/HM pocket. From the corrupted pockets, an expanded Balls pocket can be obtained in which stored PC items can be used.
In particular, TM15 executes arbitrary code from FA10 (Echo RAM for DA10), which is somewhere in the expanded Balls pocket. If "(item) x195", "Star Piece x 252" (represents C3 84 FB - a jump to FB84, box 4 name character 2) are stored at DA0F, then this will serve as a bootstrap code to stored box Pokémon names.