Lake of Rage and Team Rocket

At the Lake of Rage, save before fighting the Lv.30 shiny Gyarados. After the battle, speak to Lance and follow him to Mahogany's souvenir shop. In the hideout, defeat the two password holders, open the executive's room, and shut down the Electrode-powered generator with Lance.

Defeat Pryce's Ice team for the Glacier Badge. Elm then calls about the Radio Tower. In Goldenrod, obtain the Rocket disguise in the Underground, climb the tower, rescue the real Director from the Underground Warehouse, and use his Card Key to reach the executive.

The Director rewards you with the Rainbow Wing. This opens the earlier Ho-Oh encounter at Tin Tower; the Silver Wing for Lugia comes later in Pewter City.