Here are the next batch of rips. This time its from MMBN3.
Here are all the sprites.
This sprite is certainly unused as it supports the theory that the final room was once explorable.
The Twin viruses also have an unused eye-glowing animation. I think it isn't used because the sprite has no animations or frames in its file and it would need them if this were to be used as an animation.
As for the Rock Cubes sheet, I know I haven't played in a while but I certainly do not remember that brown cube. It isn't Desertman's because those sprites are always inside the sheet. I don't know where it came from.
From the Gutsman sheet, the overworld attacks hadn't been ripped. I'm sure it was simply forgotten. And the last line in Chisao's sheet was also missing before.