It is good to have a variety of types. I suggest strongly to have a powerful water type, a powerful fire type, a powerful grass type, a good ice type, a very powerful normal type, and last, but not least by any means, it helps to have a Luxray, at least level 72. Also, if you want to survive, bring about 15-20 revive, and just in case, after you have defeated someone, save your game.
I would say if you've got the national dex on 1 of the Pokemon games (emerald, ruby, sapphire or diamond) get a dratini as dragonite is a very powerful Pokemon and trade it to pearl. My team would be: Infernape Lvl 55, Dragonite Lvl 59, abomasnow Lvl 57, Gyarados Lvl 60, Drifblim Lvl 62 and Pikachu/Riachu Lvl 58 (that knows volt tackle)
To get volt tackle breed two a mix of pichus family (pichu pikachu and riachu) and the DAD holding the light ball. The pichu will know volt tackle.
I also think that you should have two contrasting Pokemon egg. Fire - Water, Fire-Grass, Bug-Fire. This way you can cover a large range of enemies.
The best way is challenge the elite four with your Pokemon or a Pokemon holding exp. share. The better is to use gameshark codes for rare candies.
the best Pokemon on diamond would be arceus but you can only get that from action replay, other than that i think the best Pokemon would be giritina..
the best Pokemon for the Pokemon league is definetly latios
swampert miltic
Chimchar
The best way is challenge the elite four with your Pokemon or a Pokemon holding exp. share. The better is to use gameshark codes for rare candies.
Have a good Fire and/or Ground Type...
victory road
diagla charizard lucario palkia mew and monferno
You need a grass type, a fire type, a water type, an ice type, your legendary and a ghost or dark pokemon.
Fire and water are the best combination to beat the elite 4.
NOT ACTION REPLAY!!! I say elite 4 and if you're leveling up weak pkmn, give'em an exp.share and put your strongest Pokemon in slot 1 of your party.
Diamond is not a Pokemon but i think Arceus is one of the strongest Pokemon ever.
The best thing to do is to continue to go through the elite 4 and give that Pokemon the exp. share.
the best Pokemon on diamond would be arceus but you can only get that from action replay, other than that i think the best Pokemon would be giritina..
the best Pokemon for the Pokemon league is definetly latios
the elite four. battle them over and over again or go to Iron Island. It might help!