Depends on the level of your Pokemon. BUT good places to train are the Elite 4 (Just use type difference to your advantage and WALLAH), and Mt. Silver. If your Pokemon arent up to that level yet, try Ice Path or Victory Road.
he is found at lvl 45 in Pokemon soul silver he is found at lvl 70 in Pokemon heart gold
Lvl 31
Shroomish > lvl 23 > Breloom
lvl it up to 55
Level it up until it is lvl 40.
Lvl 45
It evolves by using a Shiny Stone
magikarp will evolve at lvl 20 to a gyarados
Chikorita - Bayleef lvl 16 Bayleef - Meganium lvl 32
Lvl 15 ,, it will evolve to flaffy,, lvl 30 it will become ampharos
there is no league all you have to do is vs red at mt silver peak but he has Pokemon over lvl 80
It evolves at lvl 35 to vibrava then at lvl 45 to flygon