You have two ways to clear levels in Pengo, you can either make all three of the blocks with diamonds on them touch each other or you can use the regular blocks to squish the blob-things that fill up the levels.

But, what might not be immediately obvious is that you can use the boundaries of the stage to your advantage.

Just walk up to the edge and press the Push button. You'll cause shockwaves to go down the length of it, stunning any enemies that are near it.

Giving you a few precious seconds to formulate a counter-strategy.