A telecommunicator is located in the entrance of the Power Plant.
Ah, you're going to fight Shade...
Okay. He's at the old abandoned power plant, right? If nothing's changed, it's probably super dark up there. Shade uses that darkness to strengthen his Ghost-type attacks, but you can take a similar strategy! The machinery up there is on the fritz, and the rampant energy can give your electric attacks an extra spark! ...Or they could short it out. Either way...
But, if you can find a way to get that machinery back online during the battle, the lights should come on too! That way, you can get rid of his shadow-bases strength, and get a and get a reliable boost to you electric and steel attacks yourself!
If you get the Yureyu Key from the Byxbysion Wall (you can get it when you obtain the green crystal key at the 9th gym, and then use it at the entrance of Route 1), you can use the the keyto open both locked doors.
On the right there will be a two items; a Magnet, and TM 95 Snarl.
On the left there will be multiple Electrodes LV85. Defeat each one and interact with the computer screen. Rotom will appear as a special encounter that you can catch at LV65. If you check the summary of Rotom, you can see it belonged to Shade. You can also come here to evolve Nosepass, Magneton, and Charjabug here since this room has a special magnetic field.