Missingno.

Description
Representative of a side of the Pokémon world few dare to explore, Missingno. is an enigma. Exceedingly rare, it has eluded even the most prestigious Pokémon researchers; as such, very little in the way of official information on it is available. Missingno. possesses immense strength which it can focus into its physical attacks. Despite lacking any semblance of limbs, Missingno. is capable of punching. It also possesses psychic powers.

Volcanic islands are one's best bet for locating Missingno. Though they are commonly seen flying above the water's edge, they seem incapable of swimming.

Location

 * Mystery Gift v6.2.1: s40rf534

Shiny

 * Mystery Gift v6.3.1: 46233nc4

Shadow

 * Shadow Missingno. is not available yet.