Please help someone I can't beat the champion on Pokemon platinum my Pokemon..

I would recommend you train your Pokemon to Levels 55-60. I would also recommend you have plenty of Revives and Hyper Potions with you before you face the Pokemon League.

Spiritomb has no weakness, so you'll have to over power it. An Ice-Type Move should help you defeat her Garchomp, Roserade, and Togekiss. If your Torterra knows a Ground-Type Move, it should handle her Lucario. Torterra and Magnezone should take care of her Milotic.

Hope this helps!

When I defeated cynthia I bought lots of revives and hyper potions. And when ever one of your strong Pokemon gets knocked out, put in s Pokemon with a high defence, in your case, your magnezone. Quickly revive it and put it back to full health. Keep doing this until you beat her. When I did this I beat her first try. I hope I've been helpful.

The recommended level for Cynthia's Pokémon is 58, so you should train every one of your Pokémon except for Pelipper and Giratina (Altered Form).

Any Ice-type move will be able to make Cynthia's Garchomp faint. Her Roserade has many weaknesses They are Ice, Fire, Flying, Bug, Ground, and Psychic. Now her Togekiss is weak against Fighting, Electric, Ice, and Rock-types. Her Lucario is weak against Fire, Ground, Flying and Psychic. Finally, her Milotic can't stand Grass type moves. Teach your Pokémon any of these type of moves and she won't stand a chance!