The Forest Guardian Legendary Pokémon is Celebi and you can only get it from an upcoming event for Pokémon Diamond, Pearl, Platinum, HeartGold and SoulSilver that has yet to be announced for countries outside of Japan.
you first have to catch/defeat the legendary pokemon cobalion in mistralion cave you catch virizion in pinwheel forest
do quests and catch legendary Pokemon to get signs
You can catch it in Pinwheel Forest. But you must first encounter Cobalion in Mistralton Cave to encounter it in Pinwheel Forest.
In the Old Chatuea in Enterna forest the non legendary Pokemon are Gastly and a very odd Gengar.You can also catch them near Solaceon Town at night
You have to defeat the elite four then you can catch the legendary
you have to get more then 45 gym to catch legendary Pokemon! deoxys is a legendary Pokemon
you can catch as many legendary Pokemon but only once unless you have it on the computer
you can't catch it because you already beaten the legendary
In Ns castle,pinwheel forest,victory road,giant chasm. Thats where you catch all the legendary pokemon.
defeat all gyms,elite 4 and champion of that region to catch legendary pokemon
Check the link. Go there for the legendary pokemon.
You catch them with a ultra ball