How do you open the Pokemon league reception gate in shiny gold?

You don't open the gate to the Pokemon League Reception in Shiny Gold. It's always open!

To access the Pokemon League, you need to:

1. Defeat all eight Gym Leaders.

2. Head to the Indigo Plateau.

3. Walk through the entrance to the Pokemon League Reception.

There's no specific puzzle or interaction to open the gate. The gate is there purely to symbolize the entry point to the League.