Five question marks

????? are glitch Pokémon which appear in Generation II games. The game resorts to the error handler "?????" to name the non-existent with index numbers 000, 252, 254 and 255 if they were to appear (not including 253, since index number 253 is used for Eggs). All ????? have no cry.

List of ?????
There are eight ????? variants, differing based on the index number and version:

Hex 00

 * ????? (00)
 * ????? (00)

Hex FC

 * ????? (FC)
 * ????? (FC)

Hex FE

 * ????? (FE)
 * ????? (FE)

Hex FF

 * ????? (FF)
 * ????? (FF)

Appearance
Although all of the variants of ????? appear identical (as just a nonsensical assortment of various graphics from other parts of the game), they each use a different palette. For example, ????? (FC) appears gold and ????? (FF) appears silver. ????? (00) uses a different palette than its Crystal counterpart, ????? (00).

All variations of ????? lack their own back sprites. When a Trainer uses any variation of ?????, it will borrow the last sprite used in the battle area. This can be the original Trainer that appears before the battle starts, or another Pokémon that has been switched out. Any of these sprites will have the color palette that the particular form of ????? uses.

Since such data is undefined, the basic tileset source of the sprite of any variation of ????? depends on the last interface loaded into the game's RAM. This is usually the previous tileset basis of the main map interface, but if the player opens the Bag then closes it the game will attempt to use the menu as a source for the sprite of ?????.

Shiny ????? look identical to their regular versions.

Obtaining
All variants of ????? can be obtained through the Celebi Egg glitch or by making a clone. Sometimes a clone that was cloned multiple times becomes one of the variants of ?????. Attempting to trade 'M (00)/3TrainerPoké $ to with the Time Capsule  will cause it to appear as a ????? (00) or ????? (00). ????? (00) evolves from ????? (FC) and ????? (FE), while ????? (00) evolves from ????? (FE).

In Gold and Silver, the only way to obtain ????? (FE) is to trade with Generation I or because catching it restarts the game in a glitch dimension. That means ????? (FE) doesn't have a true Pokédex entry.

Pokédex data
In Crystal, all of the ????? glitches have Pokédex data which is undefined.

All of the ????? glitches have a footprint. The footprint is identical to that of with 256, 252, 254, or 255 printed in the middle of it for the form with the same index number (where 256 is equivalent to 0).

Time Capsule exploit
Both variants of ????? (FF) will act as 'cancel' on the party Pokémon screen, and thus can be taken into the Time Capsule to 'hide' the Pokémon below it which did not exist in Generation I.