In the Valley stage, if you knock the Mankey off the hill and then onto the switch, you will get into Professor Oak's cabin. He will start telling you that he is there in order to follow up reports that Pokémon have been sighted as landmarks on the island. He requests that you go around taking photos of these Pokémon Signs. He opens up a Pokémon Sign bit in the Pokémon Report and as such you must go and take the photos in order to access the final level.

Below is a list of the Signs and where they are found

Kingler Rock - Beach

Early in the level, if you turn your camera all the way round, you will eventually see a rock formation that looks like a Kingler. This is the Pokémon sign for this level

Pinsir's Shadow - Tunnel

Providing you have let Zapdos go, you will see a light reflecting off several beams and bolts. This will create the shadow of Pinsir. Take this photo

Koffing Gas - Volcano

Right at the start there is a volcano giving out Purple Gas. Throw a Pester Ball in there and the gas will take the shape of a Koffing

Cubone Tree - River

Near the middle of the level, there will be a Vileplume giving out a lot of gas. If you awake the Vileplume with the Pokéflut, the gas shall subside and you can see the tree

Mewtwo Constellation - Cave

In the middle of the level when the Koffing are chasing the Jigglypuff, if you look behind you when you get to the water pools, you will find a load of shining rocks. Take a photo of it and when developed they will show the Mewtwo constellation

Mt. Dugtrio - Valley

Right at the start of the course, you shall see Mount Dugtrio. Get a picture when you get closer to it.

Once all Signs have been found, Professor Oak shall tell you that a new areas had been found, the Rainbow Cloud and that it may just contain the rarest Pokémon of them all