'M (00) and MissingNo. in Red/Blue are actually the only English glitch Pokémon to be part Bird-type. The Bird-type is an unused type not to be confused with Flying-type that never made it into the final game.
When you initiate a battle with 'M (00), the battle will continue after catching it, but not defeating it. If "'M" is captured again, the battle will truly end and the Pokémon will become Ditto.
Since 'M (00)'s Pokédex number is 000, it is considered Pokémon #256. This glitch Pokémon is popular for the duplication of item #6 in the inventory. Upon encountering 'M (00) the game will look up its encounter flag beyond the end of the table and 'register the glitch Pokémon as seen in the Pokédex' by adding 128 to item #6's quantity (if already less than 128). Specifically this sets bit 0x7 of address D329.