This trick allows you to bypass the first level boss. Jump down the waterfall and battle the Blue Water Demon. Deliberately fall off the rocks and let the water sweep you to a rope that says "Grab." Jump on the rope, then press RIGHT to clear the small outcropping of rocks to your right. Let the current carry you again, and you'll end up past the boss and in the latter part of the first stage.
View Credits
For a list of credits, wait until the Psygnosis logo appears, then simultaneously press and hold A, B, C, then press START.