Offensive Mew:
* Psychic/Shadow Ball: Strong STAB attacks with good coverage.
* Flamethrower/Thunderbolt: For coverage against Psychic- and Water-types, respectively.
* Ice Beam/Blizzard: To counter Dragon- and Flying-types.
* Aura Sphere/Close Combat: For powerful physical attacks.
* Substitute/Will-O-Wisp/Thunder Wave: For support and set-up.
Defensive Mew:
* Calm Mind: Boosts Sp. Attack and Sp. Defense, turning Mew into a monstrous special attacker.
* Recover: To heal any damage taken.
* Reflect/Light Screen: To protect the team from physical/special attacks.
* Toxic/Thunder Wave: For long-term damage and paralysis.
* Psychic/Shadow Ball: To damage opponents when they come in.
Tips for Choosing Moves:
* Consider your team's weaknesses: Mew can be used to patch holes in your team's coverage.
* Think about the metagame: Which Pokemon are common in the Diamond metagame, and how can Mew counter them?
* Experiment with different move sets: Mew is incredibly adaptable, so don't be afraid to try new things.
Here are some specific move set examples:
* Special Attacker: Calm Mind, Psychic, Thunderbolt, Ice Beam
* Physical Attacker: Swords Dance, Close Combat, Aura Sphere, Shadow Claw
* Support: Substitute, Will-O-Wisp, Reflect, Thunder Wave
* Mixed Attacker: Psychic, Shadow Ball, Flamethrower, Ice Beam
Ultimately, the best moves for Mew in Pokemon Diamond are the ones that best fit your playstyle and team composition.
Important Note: Mew cannot be obtained in Pokemon Diamond through normal gameplay. You need to trade it from another game.