mareep can't be obtained in leafgreen but can be caught in emerald to trade it you need two wireless adapters and the national dex.
You'll need to transfer it from the older Pokemon DS games, or trade for it from Pokemon White.
I understand why you used " turn into." Anyway, Mareep turns into Flaffy.
trade him
you cannot get flaffy, to get a flaffy you need to have Pokemon emerald version or Pokemon colosseum and in emerald you can catch a mareep which evolves into flaffy in the safari zone in the johto area you need the national dex, in colosseum there is a shadow mareep in the game.
mareep can't be obtained in leafgreen but can be caught in emerald to trade it you need two wireless adapters and the national dex.
Number 180 in Pokemon Emerald is Flaffy the evolvtion of mareep and the pre-evolvtion of ampharos.
You can catch Mareep in Altering Cave.Mareep is not available in firered you must trade one from emerald or colosseum.
Level 15. It evolves into Flaaffy.
Since you can't get mareep in firered trade one from emerald.
After you beat the champion, the safari zone is then upgraded automatically. Go to the safari zone, there you'll see a path at rightside. Follow the path and you'll find mareep and many other Johto pokemon.
ampharos you mean right, well you can't unless you get a mareep from emerald.
in the game
There are a few electric type Pokemon you can get in ruby and sapphire and emerald like Electrike you can find a lot of them in New Mauville you can find Magnemite and Voltorb. Other electric types you can get are Pikachu, Mareep.
you can find it at valley windworks
in the secret johto area.
Train mareep