Illuminate

Illuminate is a one-Pokémon specialty held by Peakychu. With it, Peakychu can light up an entire town's worth of lamps and objects at once — far beyond what a single Generate Pokémon can do.

The ability is directly tied to the Bleak Beach storyline, where you need to "brighten things up" to wake a slumbering Mosslax and progress the main quest.

Outside of story use, Illuminate is still a spectacular way to set up a whole area of your town for nighttime without individually powering each light.