After getting the eighth gym badge, all pokémon will obey you, with the exception of Mew. The only way to make Mew obey you fully would be to use the 'Box 1 Slot 1' Mew cheat on GameShark/Action Replay.
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I have a Gameshark and the Box 1 Slot 1 cheat copies the pokemon in question but will NOT make Mew obey. If you have a Gameshark find a version of emerald and warp to Faraway island. Catch Mew, trade mew, copy mew. Now you have many mews and they obey.
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You cannot get Mew legit in Pokemon FireRed, for the event for Mew has ended. You would need to use a GameShark or trade for it from Pokemon Emerald.
A Pokémon does not obey you if it is a) traded from another game or b) carelessly hacked and you don't have the Gym Badge that makes Pokémon of its level obey. This goes for Mew as well.
How to battle mew in Fire Red. I don't know how??!!
There is none. all cheats for getting a mew are as fake as Micheal Jackson's nose
If you caught Mew by using a cheat to make it appear as a wild pokemon, it won't obey you. If you have Pokemon Emerald, you can use the 'Old Sea Chart' to get Mew properly. Another way would be to use the 'Box 1 Slot 1' Mew cheat by using a Gameshark or Action Replay.