If you trade Mew over from Emerald (or any other game you traded it too), you will be in for a shock as there is a man in XD that can help your Mew in mysterious ways. You require 5,000 PokéCoupons to do this

After you have completed the game, you will meet a guy who asks to see the "Legendary Pokémon that can learn all the attacks". Show him it and he'll ask you a few questions
If you get them right, he will give you a list of over 100 moves including some which aren't TM's or Move Tutors. You can pick only four so choose wisely

Here are the questions. Answer them and he'll generate Attacks based on your answers

What are Pokémon to you?

1) Collection
2) Treasures
3) Friends

What kind of Mew do you want?

1) A strong Mew
2) An odd Mew
3) A gentle Mew
4) Any kind

What kind of trainer are you?

1) Some victories among defeats
2) Always wins
3) Only attacks
4) Won’t give up til the end

Then his fourth and fifth could be any two of the following:

Do you want to live in Phenac or Pyrite?

1) Phenac
2) Pyrite

Who is smarter, Wazzle or Gorigan?

1) Wazzle
2) Gorigan

 Which is more evil, Cipher or Team Snagem?

1) Cipher
2) Team Snagem

 Who is a cooler Cipher admin, Aldos or Eldes?

1) Aldos
2) Eldes

Who is greater, Prof. Krane or Prof. Kaminko?

1) Krane
2) Kaminko

Who is stronger, Vander of Mt. Battle or Justy in Phenac?

1) Vander
2) Justy

Which of Miror B’s underling do you like better, Trudly or Folly?

1) Trudly
2) Folly

Which do you want, Mecha Groudon or Mecha Kyogre?

1) Mecha Groudon
2) Mecha Kyogre

With this he'll generate Movesets out of 100 Attacks. The Attacks that Mew doesn't normally learn are as follows:

Name PP Att. Acc. Type Effect
Faint Attack 20 60 -
Will always strike foe successfully
Fake Out 10 40 100
Causes Flinch, but move causes its damage and effect only on the first turn
Hypnosis 20 - 60
Causes Sleep condition
Night Shade 15 - 100
Causes damage equal to Pokémon's level regardless of other battle factors
Trick 10 - 100
Switches Foe's held item with yours
Zap Cannon 5 100 50
Causes Paralysis

The rest of the attacks shown are all of Mew's 3 Unique Level Up Moves, 58 TM/HM Moves & 30 FRLGE Move Tutor moves & the 3 XD Move Tutor Moves. Click below to view his Pokédex Entry and see them:

He'll ask you if you like the sets, if you don't then say No and it'll be re-done. This can be done over and over as many times as you want as long as you have 5,000 PokéCoupons each time