Want a Mew?
Mew is a very rare Pokemon only available through certain events and not through regular gameplay. Mew has become available through the Wii Ware game available for 1000 points 'My Pokemon Ranch' compatible outside Japan with Pokemon Diamond and Pearl only.
This game acts like a Pokemon box and as you progress you gain access to trade with Hayley for other Pokemon such as Phione (see want a manaphy or phione submission under Pokemon Diamond or Pokemon Pearl Hints) and the extremely rare Mew.
When 999 Pokémon are present in the ranch, the ranch will expand and jump to level 25, the maximum level. Once this level is obtained, a new wanted Pokémon will be added. Hayley is now asking for any Pokémon Egg. When the egg is brought, she will offer to trade it for her Mew.
Source: Bulbapedia
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