Lately, I have been wanting a mew for my diamond game. I know mew can only be obtained through events and cheats, but I was just curious if anyone knew a good way to get one. I have heard of a way to get it on yellow, but I wanted it for my newer games.
It is impossible to obtain Mew in Diamond with no Wifi. Without hacks or cheats, you must trade with a friend. It is impossible on other games, since Faraway Island is an Event that passed.
There is a few glitches in Gen 1, but since this is Diamond, that is irrelevant.
So you have to trade with a friend who has one.
Hope I Helped! (:P