Each step within the Power Plant might result in a wild Pokemon encounter. Not only do you have to worry about that, but now you have to worry about picking up items. The Poke Ball-looking spheres around the Power Plant might be items or they might be wild Voltorb and Electrode. It’s an easy way to catch those Pokemon, which might also be useful with the upcoming water-routes.
Walk into the power plant until you reach the first sphere. This is actually a Carbos. Continue north, east, and then as far south as you can go until you reach the base wall again. You should have walked through a doorway. To the right are two spheres, the one on the right being a Voltorb and the one up top being TM33 Reflect. Reflect will reduce the damage of physical attacks by 50%.
Exit out of this small office to return to the main hall. Continue east until you see another office to the south. The sphere on the left is TM25 Thunder. This is the strongest electric attack in the game, but it doesn’t have the best accuracy.
Return to the main hall and follow the path north to one more office. Inside this room are two items: a Rare Candy and an HP Up. The final thing to do is exit out of the building to the west. Follow the winding route to the exit, but don’t leave. Near the door is the Legendary Pokemon, Zapdos. This is the only one in the entire game, so do not miss it. Save your game and prepare for a lengthy battle.
Zapdos is a Legendary Pokemon. That means there is only one in the entire game, and it’s incredibly powerful. Make sure you have a ton of Ultra Balls before battle. The goal is to reduce his health as much as possible without making him faint. To increase your chances of capturing this monster, inflict the sleep status condition. Of course, it might be a little tough to do so since most Pokemon that inflict sleep are grass-types who are all weak to Zapdos’ Drill Peck. With all the previous requirements met, start chucking a ton of Ultra Balls until one finally captures him. If all your Pokemon faint, or if your run out of Poke Balls, restart your game and try again.