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You can not get a mew in Pokemon Diamond without trading or cheating (HIGHLY NOT RECCOMENDED.) but there is a way to get a mew in the following games: Pokemon Blue, Pokemon Red, or Pokemon Yellow. look up "Mew Glitch" in Google search and find out how. hope this helped!
in some cave
fishing in the safari zone is the easiest way.
Its not possible to get it legal Instant you can try to find someone who already has a mew and you'll could obtain it from Pal park that way.
The easiest way is just buy a r4.
http://trsrockin.com/mewtrick.html That's the easiest way.
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you get a master ball and catch it that way
the only way to catch mew is to defeat the elite four
cheat
The best way to catch Mew is to catch the two Shedninjas on top of the mountain. Mew is vulnerable to Ghost-type PokeAssists. Use those and couple it with a Fighting-type PokeAssist for a good chance of capture.
You have to beat the elite four and then go to cerulean cave and then you go all the way through then at the end is mew two and you have to catch it that is it
there's no possible way to catch mew in the game. you have to go to an event in REAL LIFE to get it or from wi-fi if you've already seen it.
There is no way to go into space in any of the games.
masterball
sorry no. it's fake. There is a mew and a scientist cloned mew in a movie and created mew 2. the only way there is a mew 3 if they cloned mew 2.