R-Type Final 2 (JP)

You can do this on Score Attack mode so that you start with full power-ups, and you can do it any difficulty, even Practice.

At two points during this stage, you will approach a large industrial building with a spinning fan in the wall. Inside this building there is a device which alternates between two colours: blue and orange.
(If you never let go of the fire button, you might not even know it's there).

When you shoot this device, it alters the stage.
If you shoot it when it's blue, the temperature drops and the water level rises.
If you shoot it when it's orange, the temperature rises and the water level drops.

So there are four possible routes through this stage (BB, OO, BO, OB), and each one will, at various points, present you with unique enemies that you don't find in any of the other routes.

To get this achievement, you must play all four routes and destroy at least one of each type of enemy.

Basically, this achievement will unlock if, at the end of the stage, you have unlocked entries 119-135 in the Bydo Lab.