Looking at the single screenshot given, the stage appears to be visually neat; I like how the SMB3 Fortress/ Castle tileset mixes well with the SMB1 Castle background, and the use of the Layer 3 Cave graphics for
ketchup is a nice and creative addition. It is certainly going for a dark and foreboding vibe, which is fitting for the stage's name. The only things that feel off about the stage are the Question Blocks and Mario; they're a bit too bright in relation to the rest of the stage, though that should be an easy fix.
Beyond the graphics, I don't have much to say about the stage. There isn't much going on in the given screenshot, so additional images would be needed to determine what the stage would be about or how it would play. Though this is certainly a good start. And looking at the fact that the stage already has some planning and level development, there is a good amount of promise here. I hope development for the stage continues smoothly, and that some more of the stage will be shown soon.
Anyways, I hope you have a good day and I'll see you later.