Thanks for coming back, and for the screenshots: they were exactly what I needed. The corner tiles were a wrong rectangle in the tileset (the corner of a cliff piece, scattered as "flowers") plus a second bug that punched see-through squares into the grass. Both are fixed in v0.1.9, which is up now. The map also draws about a fifth of what it did and no longer builds ground while you drag, so panning should be a lot lighter.
The freeze during plinko I still can't reproduce on desktop, so v0.1.9 has a performance readout on the backquote (`) key. If it freezes again, a screenshot of that readout, especially the memory and objects numbers, would tell me what it is.
Glad the four token kinds landed. And since you got that far: the full game (Acts II and III) is up today as a $1.99 alpha.