There are different types of gym leaders and each gym leader has a different pokemon type.
Its always good to have a range of diiferent type Pokemon. If you have any Pokemon that the gym leaders Pokemon are weak to then you should use them.
Tate and Liza the Mossdeep Gym Leaders use Psychic-type Pokemon so the best option to use would be either Dark-type Pokemon or Ghost-type Pokemon however Bug-type Pokemon will work as well additionally Steel-type Pokemon have a resistance against Psychic attacks and Steel-type attacks are super effective against Pokemon that are part Rock-type which Lunatone and Solrock are.
The gym leaders are psychic type trainers so the best type to use is a dark type Pokemon or ghost type Pokemon even a bug type Pokemon! Don't forget it will be a double battle so try using move combos.
the gym leaders are the same as they are on pearl and diamond. but the order you fight the gym leaders are different. Turtwig would be the easiest way through the game.
You have to use a cheat.
None of the gym leaders use Flying-type pokemon. If you want to face a Flying-type gym, you can battle against Winona in Ruby, Sapphire, Emerald, and the ORAS remakes. Sheβs located on the southwestern side of Fortree.
all you need is a ground type, but for octillery, maybe use an electric Pokemon or grass one, or it will slaughter your ground one otherwise
Use type matchups like for instance beating brock will be easy if you have a grass or water type. Also train your Pokemon to a decent level so it matches up to the gym leaders. If all else fails trade with friends.
The 16th gym is run by Gary. Gary, unlike the other gym leaders, does not use a specific type. His Pokemon range water to ground types. You must be ready to battle all types.
use fire
You can't. Unless you use a cheat code to catch them pokemon.
first of all, the other people in the second gym leader's gym are not gym leaders. they are just trainers who use grass-type pokemon, just like the gym leader. they are sometimes hidden behind trees and one or two is hidden in some flowers.