After concluding the Post Game Story in the Sevii Islands, you can return to Indigo Plateau to rematch the Pokemon League. The Pokemon League will continue to be comprised of the Elite Four and Kanto Region Champion, five trainers you must still defeat consecutively in order to defeat the Pokemon League. This time around, however, the members of the Pokemon League have gotten all the stronger, even switching out at least one of the Pokemon they previously had with one found in either the Johto or Hoenn Region.
The fourth and final Elite Four Member continues to be Lance, the same who remains to specialize in using Dragon Type Pokemon. He will have evolved one of his Dragonair into another Dragonite and replaced his other Dragonair will the likes of Kindgra, but the Pokemon you used to Lance last time around should still do just fine. Both of Lance's Dragonite will still be especially weak against Ice Type Attacks, and his Gyarados and Aerodactyl will still be frail to Electric Type Attacks. With all of this in mind, it would actually be best to have at least one Ice Type (for Lance's Dragon Types) and one Electric Type (for Lance's Flying Types). The only thing you will probably need to add is a Dragon Type for your own since his Kingdra is only weak against Dragon Type Attacks (though not a necessity since Electric Type and Ice Type Attacks still hit it neutrally) .
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