View Ending Sequence:
You must unlock all the levels and take photos of all Pokemon. If you do this, save your game and you will see the ending.

Access Volcano Level:
First, when you are near the exit gate in the tunnel level, throw "Pester Balls at the final Electrode. After it self-destructs, a path to the Volcano level will appear.

Access Rainbow Level:
Finish the Valley level and take photos of all six signs. The Professor will then open the Rainbow Level!