Have you made a tile that's passable to Juni and impassable to sprites yet? That would be exceptionally useful...
No, actually. There's one like that in Blox's KS mod, which can be found
here. Unfortunately, as Nifflas mentioned earlier, to make one would mean re-making a good part of the object behaviors. I know not how Bloxmaster accomplished it, but it seems to be what he did. The fact that certain bullets bounce off those walls, rather than are destroyed by them hints towards a remake of most of the behaviors, but I'm not certain.