There are good Pokemon like electabuzz and aerodactyl zapdos articuno dragonite and you have to evolve your starter Pokemon to the third evolve
The Elite Four is in the Indigo Plateau.
The elite four will be at the Pokemon league.
I would suggest fighting the elite four with a water, fire, ice, rock, electric, and fighting type pokemon.
You find him in meteor cave after beating the elite four.
The Pokemon Mansion on Cinnibar Island, and after you beat the Elite Four, Mt. Ember of the Sevvii Islands.
The types of pokemon the Elite Four use in Pokemon Y are: Steel, Fire, Dragon, and Water. The Champion uses a variety of types.
at the Pokemon leaugue
One island Pokemon centre after you defeat elite four and the 2 rockets at the volcano and find the gem.
with what pokemon, i cant answer your question if you dont tell me what pokemon
Fire and water are the best combination to beat the elite 4.
See question "Is this a good team to beat the elite four"'s answer.
You can find out how many times you have beaten the Elite Four in Pokemon Diamond by checking your PC in the game.