Hello, this is GreenBoy here. So you want a good move set for mew right? This may not be the best move set mew should have but it is good. So let’s get to it.
The first move mew should have is “transform”. If you have a opponent that is stronger than your mew, you could just transform into them. So you would deal good damage to your opponent.
The second move you should have is “me first”. If you have this attack, you can take your opponent’s move and reflect it to your opponent with times 1.5 power. So the move you copied will be 1.5 times stronger than when it was used by your opponent.
The third move you should have is “endeavor”. This move (if your hp is lower) will reduce your opponents hp low enough so it will match your hp. This is a very good move to have if your opponent is a good attacker.
The last move you should have is “Echoed Voice” because this move keeps doubling the power every time you use it. It starts of with a low power (40) but the power doubles (goes to 80 then 160 and so on). Having this is nice, but your opponent might have a really good move and might not let your power get too high (they might finish you off). For that, you can use your other moves to defend. If you are too concerned about it, then just make mew learn a attack that does a decent or a lot of damage. So if you don’t want echoed voice, you can have something like dragon claw or thunder. You could also have earthquake, but that is your only attacking move, so if there was a flying Pokémon as your opponent, you would have to use transform. If you don’t want Echoed voice, then I suggest you have the move “Sky Attack” because the move has a lot of power and good accuracy.
So here is my thinking:
(You can choose any nature but I chose Jolly)
Mew @ Expert Belt
Nature: Jolly (+ Speed and -Sp. Attack)
EVs: Should grow towards Attack and Sp.attack and Speed
-Echoed Voice/Sky Attack/Other decant move
Thank you for taking the time and patience to read it all.