[jq]if he was a legend-
he would be banned from the battle frontier
he would be hard to catch
have weird music playing when you encoutered him
although 555 is a respectable base stat it's at least 600 in a legend
but in the Anime, they thought he was in acient times[/jq]
Not all legendaries are banned, such as Latias, Latios, Zapdos, Articuno, Moltres, etc.
Some legendaries are pretty easy to catch.
Latias, Latios, Cresselia, and Shaymin all has normal music, rather then a different tune.
Anyways, Arcanine isn't legendary, only its species states it is. Arcanine was supposed to be a legendary when making generation one iirc, but I think they decided not to.