who owns the wall at the top?

The neighbor. I've searched for options like this to hide it.

I agree. That's why I was thinking of less expensive options because (1) it's so ugly and driving me crazy and (2) I'm not sure how long mediation will take before it's repaired and I need to fix the eye sore before I lose my mind.

I have no idea what that is. It's located in my neighbor's yard. He is a hostile person, so I haven't had much contact with him. All I know is he works on cars in his backyard.

Another suggestion would be to sacrifice a foot of your property and put up a nice wood fence on your side of the wall. You will only see your fence and loose a small bit of space, it its not an issue, I think it might be worth the stress of trying to work with a difficult neighbour.

find out how tall of a fence you are allowed to put in your yard. odds are not all of the way to the top. but you could build a lattice structure as well, like a pergola with a latticed back.

if you google 'lattice backed pergola' there are a lot of photos of projects that would work for you. the idea is to have something nice to look at before your eye hits the eyesore in the way back.

What are your plans for the yard? I'd put up a few fast growing trees, however, if they drop leaves in his yard, he might get mad.

I agree a fence might be a good idea, don't they say fences make good neighbours? I wonder if that white thing is even on his property, looks like it's been pushed out. It looks like there was a tree there which probably helped to bring down that concrete wall. A cheap no build option is virginia creeper but you'd still have that white bin right there.

That wall looks dangerous. Was there a fire or something?
I think the first thing you need to do is get the stump removed and then level out the yard.

I'd be hesitant to put up a fence because it looks like the block wall is about to collapse at any time.

Vatrice, you are in a precarious position. A hostile neighbor is always a big problem. Don't know where you live, but a situation like this would normally warrant going to your local city or county and filing a complaint in the Code Violation office. Then someone would come out and view the situation and determine if the falling down wall is a code violation. Looks dangerous to me.

What did you end up doing?