If you want to access the eight new levels, you need to collect all eight “Rare” orbs throughout the game.
By far the hardest red switch to find is in 7-5 Cog Jog - when you reach a gear with a downwards banana arrow (which is easy to miss), pound the ground to roll the wheel and access the barrel. If you beat each stage and are confused why you can’t progress, simply go back and locate the hidden barrel to each button room. In World 7, you have to hit the three red switches inside the world map square.
