At least it (sorta) blends. There was some effort to maintain the shape and colour of the brain (if not the pattern), the slate-blue background (although it doesn't match the grey sky in C1). I'm sad that the floating platform in the center was left deformed and unfinished.
I do think that taking the last three contiguous panels in a level as a block is bad colab-form. (I've done it myself, and will almost certainly do it again, but still think it's bad form.) Also, I think the
"simply flip the square you're butting up against, and chip away/draw on top of it"
method of blending is lazy. (Again, I've done it myself, and will almost certainly do it again, but I still think it's lazy.)
So, all in all, a somewhat disappointing finish to 3266, but I've seen (and done) much, much worse in the history of the cosm.