Secret characters in Parappa The Rapper?

The instruction manual contains a tip mentioning secret characters of some sort. I looked it up online, and a website stated that Sunny and a Ninja become playable after certain requirements are met. The book did mention a ninja, so I kinda believe them, but I'm not sure how to unlock these characters. I tried what it said on the website, but stage 2's requirement is darn near impossible; finish the level with the cool mode icon flashing. But as the icons only flash every other set of buttons, it's impossible to do. Please! Can anyone explain this to me?