After exploring the basement, Mikey stumbles upon a hidden passageway that lies between stages. There are no keys to collect, but there are a number of hidden surprises. Bats and skeletons haunt this area and guard the diamond treasures it keeps.
This short passage is actually the longest out of them all. It is the only passage broken up into two parts. The path to the upper left is completely option, but worth the trip. Bats appear constantly and skeletons dig themselves out from the ground. Sometimes their whole body comes up, and sometimes it's just the head. Deal with them both carefully.
Two large sets of four diamonds are easy to discover in this passageway. However, you'll soon learn that only three diamonds will appear on the screen at one time. In order to reveal all four, you must collect at least one of them before proceeding. Grab the four in the upper left region and head down to the vine that leads to the second half. Just before climb down, you can make a special guest appear.
Early on in Konami's history, they decided to create a mascot known as Konamiman. He looked a bit like Superman, but he wore a horned helmet. If you provide the correct input just before the vine that leads down to the second part of the passage, Konamiman will fly across the screen from right to left, and you can collect him for an easy 5000 points.