You can use any Pokemon. As far as I know you don't have to use certain Pokemon to challange them.
Ghost, Fire, Ground, Psychic, and Ice
I would recommend Pokémon lvl. 56 or higher. (Reccomendations: lvl. 60.)
To get to the Pokemon League in Firered/Leafgreen. You must have all 8 gym badges, have a team that knows all HM's(you'll need them), and a strong team to get past the trainers. Best of luck. Pokemon Master Chewie.
must obtain the required number of league badges
skill
You have to beat the league.
Get 8 badges
if its the ace trainer then you need all 8 badges to get past him :-)
tecnically in sunyshore or other city, but then you need to beat the elite 4 in the pokemon league, past that city.
The Pokemon league is in the north of Opecuilid city, past the victory road. The HMs you will need in the victory road are: -Strength There are very little trainers in the victory road, and it's mostly a giant maze. This is also a good place to pick up some useful TMs to use in the Pokemon league.
Go to sunyshore city, then go up in the water (make sure you got surf and waterfall) to swim and to go up the waterfall to The Pokemon League then you will reach a Pokemon league cave past it and then go to the Pokemon league heal your Pokemon and fight
Well, you just need high level pokemon, some full restores, and status healers. Or use the walk through walls AR code.