New Section of the Nether Fortress- Dark Tunnel

Nether fortresses are somewhat bland because they are entirely composed of 1 block type. One idea to improve this is to add a variant of the covered section with black concrete on the inner walls as opposed to nether brick. When connecting to an inside section, there would be strips of black concrete of differing length replacing the nether brick at the transition section, similar to the broken design that nether fortresses end with today. This make the dark tunnel look like a black entity taking over the fortress. Inside this section, the design would be similar to the current roofed portion of the nether fortress. However, the texture of the black concrete would make the walls and staircases impossible to see without lighting, making it a navigational challenge. Only wither skeletons would spawn here, and would appear much more frequently than anywhere else in the fortress. They would blend into the black concrete very well, making them difficult to fight. To re-balance the fact that this place would be so easy for wither skeleton hunting/farming, 1/5 of the wither skeletons that spawn here would be armed with a bow and shoot flaming arrows that also apply the wither effect. Very rarely, a prize could be found in this section- a "tree" with a trunk of 3 blocks of ancient debris and 5 glowstone leaves at the top, planted in soul soil. On the outside of this section, an additional layer of nether bricks would hide the black concrete so it wouldn't look glaringly out of place.