The Nightmare-B is a mysterious weapon that was produced in the Underworld. To obtain it, you must be on mission 16 and have Double Jump from Alastor. When you begin the level, go up on the platform, and exit out the only door. You will see blue torches on the ground lit. Find the one side of the level with arc openings. When facing with the back wall inside, turn left to enter the room (where blue shield was located) follow the path through, make it through the forcing spikes, and you will reach to a dead end with a object glowing at the end and deadly toxins on the bottom. Jump onto the only platform, then use Double Jump to get Nightmare-B (must have Alastor equipped). This weapon is very powerful against the blob when he is transformed. However, it takes up one Devil Trigger.