Articuno
Go to the Cave level and follow it almost to the end. Then when you see the
Jynxs play the Pokémon Flute. The Jynxs will perform a ritual dance, and the
ice egg will float in the air and hatch into Articuno.

Charizard
Go to the Volcano level and follow it almost to the end. Then, throw an apple
at the Charmeleon that is near the lava pool. It will evolve into a Charizard
after being knocked into the lava.

Gyarados
Go to the Valley level and hit the Magikarp that is in the water in front of
the first Mankey. Then, Mankey will hit it over the mountain and onto land.
Later, when you are in front of the three Gravelers, hit the Magikarp with a
Pester Ball. Magikarp will go over to the waterfall evolve into Gyarados.

Haunter
Take a picture of the purplish mist in the first part of the Tunnel. Then a
Haunter will appear when the picture is developed.

Moltres
Go to the Volcano level and follow the path until reaching an egg in the middle
of the road. Throw an apple at the egg to make it fall into the lava and
Moltres will appear. Note: Wait for it to face you for additional points.

Muk
Shoot gas bombs at the Grimmer in the Cave level to evolve it into a Muk.

Zapdos
Go to the Tunnel. Then just after the first door you will see a Pikachu next to
a large egg in the distance. Throw some apples to lure the Pikachu closer to
the egg. When Pikachu gets close enough, play the Pokémon Flute. Pikachu will
start an electric attack and zap the egg. The egg will hatch and Zapdos will
appear. Note: You will need Zapdos to shock the generator if you want the
Pokémon sign.

Finding the six Pokémon signs
After completing the Valley level by hitting the Mankey on the switch,
Professor Oak will tell you to take pictures. Here are their locations:

Kingler
On the Beach level, after passing Pikachu, turn around and take a picture of
the rock with seaweed that resembles a crab.

Pinsir
In the Tunnel, wait until Zapdos has hatched and turns on the power. Then when
you pass the Electabuzzes and Pikachu, look to your right to see Pinsir's
shadow on the wall.

Koffing
In the Volcano level, throw a Pester Ball into the small volcano to the left of
the first Rapidash that appears. Then, smoke in the shape of Koffing will
appear.

Cubone
In the River level, play the Pokémon Flute in front of the sleeping Vileplume.
Then the smoke will disappear and a tree in the shape of Cubone will appear.

Mewtwo
In the Cave level, after hitting the two Koffings chasing Jigglypuff with
apples, turn around to the left while near Weepinbell to see some bright
crystals/stars. Then, take a picture and it will turn out to be Mewtwo.

Dugtrio
In the start of the Valley level, take a picture of the mountain behind the
Mankey.

Rainbow level
Successfully complete the Valley level and take pictures of all six Pokémon
signs. Then, Professor Oak will open the Rainbow Course with Mew. It is very
hard to capture, but is worth a lot of points.