I had an idea while I was on the bus today. On the waterfall that you climb up to get to the Pokemon League there could've been a cave hidden behind it. Inside is basically a regular old dungeon like the Whirl Islands dungeon and as you get deeper into the dungeon you reach 3 stone pillars each pillar asks you to bring it something. The first pillar asks you to bring Sea Ice. The second, Eastern Lightning, the third asks you to bring it Victory Flames. And each pillar gives you a hint on how to find them. One each pillar you see the same etching (lines and squares) but each pillar has a red circle on a part of the etching. Veteran Pokemon players my understand the etchings. Basically what you have to do is catch the legendary birds in Sinnoh. Once you get all of them put them in your party take them to the pillar room. The pillars will be glowing blue, yellow, and red respectively. When you interact with the first one you will get a message saying" Articuno is getting restless let it out of it's Pokeball?" Y/N. Then when you let it out it will freeze the pillar. Then the pillar will disappear. The same thing will happen with Zapdos and Moltres. Then when all the pillars are gone you will be able to enter the next room. Use Waterfall then surf ahead and you will see Lugia.
I'll shed some light on this. The etchings were a line map of Kanto. The red circles were circled around the areas where you found the legendary birds in Red, Blue and, Yellow. i named the elements needed to get rid of the pillars after the areas aswell. Sea Ice refers to the Seafoam Islands, Eastern Lightning refers to the Power Plant which is on the eastern side of Kanto, and Victory Flames since Moltres was found in Victory Road and Moltres' fire is used to light the torch at the Pokemon League.
This will also give reason to the birds' appearance in the Sinnoh region. Lugia has awakened and needed it's servants, but only a powerful trainer can bring them to Lugia.
