These are the bonus stages in Pokemon Pinball. There are 2 bonus stages for the red board and 2 for the blue board. Theres even a special stage.
Red Board:
Diglett Stage
Take out all 31 Diglett and face the Dugtrio. When facing Dugtrio hit him 3 times to clear the stage.
Gengar Stage
hit all the Gastly. Once defeated you will face two Haunter. After defeating the 2 Haunter you face Gengar. Beat Gengar to clear the stage.
Blue Board:
Seel Stage
Hit all the Seel in the Water 20 times to clear stage.
Meowth Stage
Meowth is carrying a bunch of charms. Make him drop them and collect them to clear the stage.
Mewtwo Stage
To get this bonus you must clear the first bonus stages on the red and blue boards. To beat him hit him 25 times. The forcefield makes this stage very hard.