Use the VS Seeker near the Hot springs in one island. There are several trainers there.
Level them up
there is no good Pokemon and bad Pokemon its just the way You level it up and what moves it knows /execpt Magikarp they cant learn moves but Gyrados is worth it at the end.
Yes it is in a cave.
No way you can't get a johto starter Pokemon in Pokemon leafgreen. The only way is to trade with someone to get it.
sorry. There is no way to get to johto with Pokemon leaf.
You can only get inside when you fight finish the Pokemon league .
The fastest way I know is Exp. share. A really easy way is to put your highest level Pokemon in front and give the Exp. share to a weak Pokemon (Level 1-25). Go to Victory Road (fly to Indigo Plateau) and defeat as many Pokemon as possible. Another way for higher-leveled Pokemon is to defeat as many people as possible using the Vs. seeker. You put it in front and find an area with Pokemon around the same level (or weaker). That should work.
Mamoswine doesn't evolve either way because it doesn't exist in Pokemon LeafGreen. It evolves from Piloswine who evolves from Swinub, but Piloswine can't evolve into Mamoswine in LeafGreen.
There is an easy way to get your Pokemon to a certain level. All you need to do is collect rare candy and use it on the Pokemon you want to level. This will automatically level up your Pokemon.
just train your Pokemon each to lvl 55 and you should have no trouble
You can't. In no way is it possible to get Totodile in LeafGreen.
Level them up
Yeah go to route 1 until you find it then use the masterball.
There is only 386 Pokemon. Counting event Pokemon and the Sinnoh Pokedex, there are 493 Pokemon in current existance. However, ther are still many on the way. 107 of these Pokemon cannot be caught or traded to LeafGreen. Not really. There is no easy way to do anything in the Pokemon games. After all, if everything was easy, there would be no challenge and Pokemon wouldn't be as fun. If you are desperate, however, consider using a cheat device such as a Gameshark or Action Replay.
There is no easy way to beat the Elite Four. You have to level up your Pokemon and use the right types of Pokemon against each of the elite four (i.e. don't use a fire-type Pokemon against water-type. Use electric instead). I recommend level 60 or so for the Elites. Good luck!
you can give them a lot of rare candies
keep battling Pokemon and people