[Kamaeru]

I can think of a few approaches you could use to accomplish it, but no matter what you'd have to be creative and create a hack of a solution. From having 2 sets of the wall tiles, the second on swimmable tile indices on the tileset, to making the walls npcs. There is no way to do legit layers on graal without some sort of scripted solution or visual trickery. But I could pull it off while maintaining the illusion of layers yeah. Sometimes when something seems impossible with the scripting engine, you have to remember there are also scripted ganis you can do a lot with.

It would be possible to use a special tileset where the underwater wall tiles would be swimmable tiles, and then have a script triggered by a level variable to update the board every time it switches.

The problem with that however is that there are not many swimmable tiles on the tileset. Perhaps you can use setshape2 to make it detect as water tiles.

There are easier ways to do it like warp the player to a different level, or just make the underwater wall tiles drawunderplayer images, or to not even show the walls underwater.

As far as changing it so that you can walk over blocking tiles, setshape2 does that. You can save the array for setshape2 into a variable and reload it using something like setshape2(x,y,this.array), making it so you could save 2 arrays, one for before the change and one for after.