Quick note,
Articuno is in a cave in the Ice cave between Mahogany/Blackthorn, in its own little entrance surfing south of the first bridge east of mahogany.
Zapdos is in the rock tunnel, quite simple to find from either entrance just run straight through w/ repels.
Moltres I believe is in Mt. Mortar, can't recall directions.
Now I'm pretty sure only a few people have found this little egg in the game.
Inside of the undersea caverns, there's this place called the Fighting Dojo. Basically you fight all 17 types of pokemon, 6 for each person. So 6 fire, 6 water, you get the point.
I love this! Except they're level 100 so I have no idea what this 'prize' is.
That's one of the great things about this game, the hidden stuff. That articuno cave, I would have never found it if I didn't bother surfing at an area most of us wouldn't even bother at.
One more thing, on the official release from christmas 2011, I had played that to completion. One puzzle had still baffled me. I can't recall the name of it, it was southwest of cherry grove. Lost woods maybe? When you went inside you would here weird sounds, and you were supposed to walk in a certain pattern. I still don't get this puzzle, could someone explain?