Zapdos

Fly to the Epidimy Town Pokémon Center and go to the town’s southeast corner.

Enter Thundercap Mountain.

Once inside, follow the linear path forward.

You’ll come across a ladder you want to take to the upper floor.

On this new floor, take the stairs directly east of you to get on a rocky platform and follow the path north.

Get off the platform from the other side and walk northeast toward the area with movable boulders.

Use Strength to pass the boulders.

Then ignore the stairs to the east and follow the northeast path instead.

You’ll eventually come across a small set of stairs at the end of the path. Climb them and then continue east.

Walk past the blue and white bridge and take the ladder to the upper floor.

On the upper floor, Surf directly east.

Take the ladder you see at the end of the path east.

Follow the single linear path forward to progress.

The ladder taking you to the mountain’s peak is at the end of the path next to a Chansey who can heal your Pokémon.

After climbing up, take the path east.

Continue following the path filled with multiple stairs.

Get to the top of the mountain’s peak where you’ll get the prompt to call out to Zapdos.

Select “yes” and Zapdos will appear to challenge you.