How do you beat the Elite 4 in Diamond?

Here is how to beat the Elite 4. Pokémon that are Level 70 or over are recommended. This is one of the best teams:

Infernape Moves: Flamethrower- Close Combat- Flare Blitz- Flame wheel

Empoleon Moves: Hydro Pump- Surf- Drill Pack- Bubblebeam

Luxray moves: Discharge- Crunch- Thunder- Thunderbolt

Garchomp moves: Dragon Claw- Earthquake- Dragon rush- Dragon Pulse

Lucario moves: Aura Sphere- Dragon Pulse- Close Combat- ExtremeSpeed

If Diamond, Dialga moves: Flash Cannon- Roar of time- Dragon Claw- Draco Meteor

If Pearl, Palkia moves: Aqua Tail (if lv 80)- Spacial Rend- Dragon Claw- Draco Meteor I suggest you use a Fire type (Infernape) for the first Elite Four since he has Bug type Pokémon. His strongest Pokémon is Drapion so watch out. For the second Elite Four, I would use a water type (Empoleon) because she has Ground type Pokémon. Also, Hippowdon is her strongest Pokémon and the Sandstorm does not affect Empoleon. For the 3rd, use a water type for his 3 fire type Pokemon, a fire type for Steelix and a fighting type (Lucario) for Lopuny. Lucian, any Pokémon will do. Like you saw in the episode, Bronzong is his strongest Pokemon. For Cynthia, a mix.

Answer

The first to fight in the Elite Four: Aaron-Bug Trainer: You should have a Fire Type Pokemon in your Team! Just use Fire attacks on this one and you'll be fine!

Second Elite: Bertha-Ground/Rock Trainer: You should also have a Water Type in your Team, I would recommend these moves, Surf, Hydro Pump, Waterfall, and another one that you happen to like.

Third Elite: Flint-Fire Trainer: Use your Water Type Pokemon again. This should be very easy since Water beats Fire.

Fourth Elite: Lucian-Psychic Trainer: What would be best is the TM Earthquake. If you already have one then you're in luck! That will kill mostly all of his Pokemon. Except Bronzong since he can levitate. When you get to Bronzong use your Fire Type Pokemon and use a fire attack he'll go out in one shot!

Cynthia/ Champion: She has six Pokemon there's 1) Spiritomb-Use either a Ghost/Dragon attack 2) Gastrodon-You could use a lightning attack on this one. 3) Milotic-Thunder will work 4) Garchomp-Use Ice attacks on this one 5) Lucario-Wipe it out with Earthquake 6) Roserade- Use a Fire attack!

I also want to mention that the Elite Four and the Champion' Pokemon will be all at Level 53-66 in other words you should get your Pokemon to at least 70 or else you'll never win this game.