?'s cry is identical to that of Unown. Its only move is Tackle and it is incapable of learning any others. It has no Ability, displayed with the name ------- and the description "No special ability" on the status screen.
Its Pokédex entry points to garbage data. It has a unique footprint, a generic paw-print with a question mark inside.
?'s sprite was originally coded to represent an unseen Pokémon in the Pokédex, as seen in pre-release screenshots of Ruby and Sapphire. However, developers later changed the "unseen Pokémon" sprite to that of ??????????.
? is a very stable glitch and does not cause any undesired effects on its own. However, attempting to cheat moves onto it will cause save data to corrupt and be deleted.
It can't be transferred to Generation IV via Pal Park, with the game giving the message "You can't transfer this Pokémon".
This Pokémon was unavailable prior to Generation III.