Against the Elite Four in Platinum i use:
Staraptor-Lv.90
Heatran-Lv.90
Empoleon-Lv.95
Dialga-Lv.90
Palkia-Lv.90
Giratina-Lv.90
It's easy with these Pokemon or any Pokemon really around these sort of levels.
your strongest Pokemon
There aren't specific Pokemon for battles.You should use your strongest Pokemon.
you should use water types because they are strong against fire types
See question "Is this a good team to beat the elite four"'s answer.
The elite fours Pokemon are all lvl 50ish so have a good team at about lvl55+ and you should be okay I recommend taking a dark Pokemon because it will be super effective against two of them the elite four are types are, ghost phychic dark and fighting you can fight them in any order you want
You should rebattle the Elite Four over and over. You should rebattle the Elite Four over and over swapping out every Pokemon in your party.
level 55 and up and ever type of Pokemon
try going in the elite four with Pokemon lv. 60-100....
they should be lvl 55-62
50 and over.
There is no easy way to beat the Elite Four. You have to level up your Pokemon and use the right types of Pokemon against each of the elite four (i.e. don't use a fire-type Pokemon against water-type. Use electric instead). I recommend level 60 or so for the Elites. Good luck!
weedle, sparrow, geodude, nosapass, skitty