
Ditto
Type: Normal
Ability:Limber- The Pokémon is protected from paralysis
Imposter- You transform into the Pokémon in front of you
Base Stats: Hp/Atk/Def/Sp.Atk/Sp.Def/Spe
48/48/48/48/48/48 Total: 288
Moves: Transform
Ditto is the kind of Pokemon that you can use abuse the strengths of your opponent. Using the impostor ability, you get to transform upon entry and then use one of your opponent's moves. This also copies all stat changes and EVs except changes in HP.
This is best used against Mega-Evolutions, where you still have an open slot for items. It's also decent against everything else, especially if the opponent has moves that it's weak to (i.e. dragonite with draco meteor). So anyway, here's two "sets"
Anti-Mega
Ability: Imposter
Nature: Hasty/Naive (pick your poison)
Moves: Transform
Item: Life Orb
This set is to transform into a mega-evolved Pokemon. With a speed-increasing nature and damage-boosting life orb, you can hit mega-evolutions fast and hard.
Tank-Copy
Abilty: Imposter
Nature: Bold/Impish (you know the drill)
Moves: Transform
Item: Leftovers
Ditto becomes a tank, but is still viable as a slightly bulky attacker. Leftovers is a good boost for longevity in any case.
All in all, Ditto is more of a gimmick that works perfectly under certain conditions. Since its properties are not set in stone, it can add some versatility to your team.