Part 25: Level 20
Featured music - "Fascination Street", "Prayers for Rain", and "Disintegration" from Disintegration by The Cure, "Bigcore MK-III" from Gradius V Soundtracks by Konami, and "Thunderbolt" from Salamander by Konami and rearranged by Snappleman.
This mine can be a bit of a doozey. The mine is a gauntlet of cage matches in tunnels as well as large rooms that release robots from hidden doors upon getting a key. Always be ready for a surprise to happen here. The door on the right at the beginning of the mine can only be opened once, so don't miss out if you want those precious, precious points.
Also, it's time for a boss.
Unlike the last two bosses before it, this one is only weak to energy-based weapons instead. The only secondary weapons that can damage it are the bomblets released by smart missiles and smart mines. This boss will fight back with smart missiles, so use the corners to avoid them. The best way to fight it is to hide and fire a volley of phoenix cannon shots and have them ricochet into the boss.
You will also see the second secret exit to secret level five while fighting this boss. I believe that this teleport is there just to give a new player an opportunity to explore one if they haven't found one yet. This is the only easy one to find. You can hide inside the teleport room if you have cleared the secret level already, but the robots might be able to see you, so use caution. I do not recommend using this as an alternate exit from the mine once you destroy the boss robot. Instead, use the normal exit and remember to shoot the control panel inside the tunnel before exiting the mine. There are two earthshaker missiles that will be revealed in the same room and this is the only way to get them, because you're going to need them soon.