There are three Pikachu. One outside at the start where if you take multiple photos it will jump on an Electode and roll with it making for a good photo. Later on it is also by a Zapdos Egg. Use the PokéFlute to encourage Pikachu to Thundershock and break the Egg open. After that there is one by the Diglett

Electrode is a rather common Pokémon found throughout the tunnel. They can be caught rolling around or staying still. However throw an item at them and they will blow up which makes for a good picture

Firstly found chasing an Electrode into the Tunnel, it is primarily found inside and can be hit with an Apple and use its Electric Shock to activate computers and for good pictures

Kakuna are in the entrace of the Tunnel on the ceiling. However they are constantly falling down so you should be able to get a good photo of a few of them together after this

If you use the Pokéflute by Pikachu and the giant egg, Zapdos will hatch and start powering up a generator. This makes for a great shot

There is a small bit of water by the Zapdos Generator. Throw items in to get Magikarp to jump out

Haunter isn't seen in the level itself but a Purple Aura is seen flying about in 2 parts of the level, take a photo and it will develop as Haunter

Zubat is seen once very quickly as you go through a door it will fly at you so you'll have to take a quick picture

Nearer the end of the level, Diglett is seen playing with Pikachu

Take a picture of each Diglett and eventually a Dugtrio will appear

Magnemite is found at the end of the level. However, if you try to take a picture it will create interference and prvent the picture. Lure it with an apple and you should be able to take the photo

Magneton is found by lureing the 3 Magnemite together. It will fuse and become a Magneton