When you’re exploring a Pokémon’s natural environment in Pokémon Snap, almost anything can happen while watching them. For many encounters, you need to see them while embarking on a particular route or using one of the items available to you inside the NEO-ONE. When attempting to complete A Light in the Depths request, you’ll need to take a picture of a Lanturn surrounded by Frillish. You can grab this photograph in the Maricopia region on the Lental Seafloor tour.
The specific route that contains this Lanturn is on the left pathway of the map. To reach this pathway, you need to use an Illumina orb on a Clawitzer attempting to destroy some rocks. The Illumina orb provides the Pokémon with the strength to shatter this object, granting you passage on the left side of the map.
Once you’re going down this route, the interaction won’t happen for quite some time. You’re better off looking around, taking a few pictures, and waiting until the NEO-ONE starts to bring you further down. You want to wait for the moment a Sharkpedo rushes after a Lanturn, and then a Wailord brushes past your device. After this, look around for a Lanturn on either side of a male and female Frillish. The Frillish will be tickling the Lanturn, and you need to take a picture of it to complete the request. It might be a little difficult because there are several Wailmers swimming by. You want to make sure the picture features Lanturn, too. If it does not feature Lanturn, and it’s focused on Frillish, it doesn’t count for the request.
After you capture the picture, proceed through the rest of the route and make your way back to the research center. Click on the ‘Y’ button and go to the requests tab, turning the quest in to Phil.