Shiny Meltan became available again from April 24th, 2019 until May 5th, 2019.
Most of Meltan's body is made from liquid metal, and its shape is very fluid. It can use its liquid arms and legs to corrode metal and absorb it into its own body.
Meltan generates electricity using the metal it absorbs from outside sources. It uses this electricity as an energy source and also as an attack that can be fired from its eye.
Clearly a curious Pokémon, Meltan is very expressive and shows an interest in all kinds of things.
Its name was originally displayed as "???" in gameplay and in game data it was referred either as "Pokémon 891" or "Kecleon", the second one was because of Meltan being initially released in the game by replacement of Kecleon assets before its own were added to game files.
Additionally, following names were given for this Pokémon in player community before its official name was announced: "Nutto", "Nutface", "Incogditto", and “DittoNut”. All of these nicknames refer to either its nut-shaped head or its resemblance to Ditto.
Its small, silver body resembles Ditto and a hardware nut-shaped head with an eye floating inside, which when displayed in nearby as shadow silhouette resembles Unown.
There are sound files of Meltan's and Melmetal's cries in game assets. These files are called "pv891.wav" and "pv892.wav" and they implied that Meltan's National Pokédex entry number could be 891, which could confirm at least 86 new Pokémon species introduced in Generation VIII of the core games series, however after final release of this Pokémon to the game its Pokédex number was revealed to be #808.