Is there a term for the kind of magick that specializes in negative existence instead of positive existence?
I'd still call things like death positive existence. Maybe this is edgy in a different sort of way. The kind of spell work that's slightly insane, but neither dreary, nor manic.
An example: a kill spell
Rather than focus on destroying the body, with the idea of deconstruction in mind, treat the death like a meaningless puzzle. Suppose a person is one of those types of puzzles where there's one piece missing and you slide them around. Where I'd expect black magick to just burn the puzzle up, to achieve an end. This kind of magick would scramble the puzzle, continuously looking for ways to viciously defile it in the most interesting ways. I wouldn't even call it destructive, more like "sick" and creative, but mostly apathetic, not inherently malicious.
I'm thinking of the kind of magick that, instead of teaching to learn imagination, to visualize plastically, etc., would first teach you how to un-imagine first. That is, rather than add objects to your perspective, remove them. Like being taught the eraser before the pencil.
Where you learn to disassemble yourself before you learn to reassemble anything. Learning faster than ever through deconstruction, but also risking far more than is probably necessary, just for the sake of efficiency.
If you were to astral project in "positive existence" magick, in "negative existence" magick, you would learn to dissociate, depersonalize, reach backwards from ascension. A sort of ascension in an opposite manner. A descension. Rather than be "enlightened" and see that there is more than meets the eye, expanding consciousness, learn to compress it, fully understanding the workings from the "bottom up" (versus top down), closer to the hardware, what it means to be a lower life form.
I wouldn't call it evil either though. Just an opposite perspective. Rather than heal a wound, kill the sickness. Rather than draw the adjective "healthy", erase the adjective "sick".