On a whim, I put a solid row of grass on rows 0 and 255, and a solid row of ocean border next to it. It seemed to be okay with that. If you get it to break again, it would be awesome if you could send a screenshot. :)
Will do! Meant to reply to this weeks ago, but between lack of time at some points and jumping between projects I've been working on I seem to have completely forgotten to.

Glad to hear adding a single row to the top and bottom doesn't break anything! Perhaps I broke it by going overboard and having like, 4-5 rows on the top and bottom, plus a shit ton of jagged points haha.
I'll redo my edits here in a little bit, and I'll post screenshots of what it looks like in the editor before testing, and what happens in game. :D
EDIT: Well, seems the "shitload of jagged points" must've been what caused my rom to shit itself. I've got 7 solid rows of grass tile on the top n bottom of the world map with no crashing!
Granted, that's not a very big landmass height-wise, but it's looking like my idea to have a small continent on the outer edges of the world map is more plausible than I originally thought!
Also, THANK YOU for having the tile properties in your editor. I recently changed the hovercraft in my project to a ship, and between Chillyfeez's vehicle knowledge and your editor it was absurdly easy to set up!