Diamond Rush Perfect Walkthrough: Tibet or Siberia Secret Stage 2

Keep the monkey on the area where the golden key chest is. Just make sure he is locked there before crossing the snakes. It's much easier dealing with him this way.
About this walkthrough: I call it "perfect" because it shows you how to get the 4 possible perfect messages (all purple and red diamonds, no hits or retries) on every stage in the game.