Sewer and jail sounds great.  the main character could get captured, escape the jail by killing guards, and get to a sewer hatch.  Then he has to get out of the sewer.

I like the jail idea, and indeed there is one jail scene so I could have 1 jail level.  But the sewer, despite being a wonderful idea, would be too similar in appearence to the factory textures I have

What about having it lead into a forest? Can the rendering engine handle variable-height walls like DOOM could? That'd be kind of cool, and have very different textures. If not.....Maybe have the Jail lead up into a big castle?

ok, sadfaceness.

How about a mine? That would have quite a different look from a cave or dungeon, since it would have both the roughness of rock and earth, and the manmade structures, like wall supports.

I think I MIGHT have a cool trick to make a "Kamino" world work.  I'm not going to test it now, but if the trick for smaller walls works, I'll do the platform water world, as well as a "Cloud City" world.  It will also make the space levels more fun

I you have a water world, will you be able to use some sort of wave effect?

If you have the screen content updated completely every frame, what I thought was something like in ROL4 (discontinued) which only involved offsetting some rows of the screen by 1 pixel to the right or left. However in ASM it might be harder, since it's not a multiple of 8 (xLIB did the dirty work for me)

THat could work too I guess, although I wonder if it would look like water...

Oh I see . I guess you could definitively just use some sort of small tilemap or even sprites.