There is a point in the Iceman stage where you try to get a 1-up but often miss it. When you drop down to the next screen (the one before the Big Eye), use your magnet beam and try to climb your way up and try to hop onto the offscreen platform where the 1-up is supposed to be. The moment you step on it, the screen will glitch and show you falling to the screen below and avoiding the Big Eye in the process.