If Ruinses is proper, then Ruins must be singular as well.
Somehow I feel the need to explain this stuff even after saying how pointless that would be. That is what the internet does to a man.
In the sentence "Ruined Village is a Ruins," "Ruins" is singular. You can tell from the "a!" Note despite being a former computer programmer that I put the exclamation point inside the quotes. If you then wanted to say what Ruined Village and Abandoned Mine collectively are, that would be "Ruinses." As usual despite being pretty sure of this I used the internet to verify it before using the word in the preview. If you aren't reading this from a print-out then this power is available to you as well.
If you see the movie Holes, did you see two movies? When you say "I saw Holes," that's shorthand for "I saw the movie named Holes." It's one movie; Holes in this context is singular. The fact that the movie's name is also a plural English word doesn't change that. If the director made another movie very similar to Holes, and then a third, then you might say, "man, I wish he would stop making so many Holeses."
The entire point to me saying Ruinses in the first place, in the preview and wherever afterwards, was because, it's funny. It's funny that the plural is Ruinses, because no-one would actually say Ruinses, and they would sound like Gollum (a character created by a linguist) if they did. Death Cart doesn't say Ruinses, because it would look weird; we don't have someone forcing us to adhere to a particular style guide, although Jay decided to go light on contractions (I disagree there) and to say "he" for indeterminate gender (I prefer "they" like a normal person).
It has not been so common to pluralize proper nouns in the past, but it comes up a lot with card games with named cards. You have this name, it's some ordinary real thing, but it's a name, it's proper, and the style guides say your Magic deck has four City of Brasses and four Llanowar Elveses, not four Cities of Brass and four Llanowar Elves. Normal people say Cities and Elves and that may well be the wave of the future. If you see a newspaper article telling you how many times Madonna won a Grammy though, they will call them Grammys, not Grammies; once it's proper they just add -s or -es.