I made these tiles while I was working on Goriya Rebellion. These are ducts that may be used in dungeons, although, theoretically, they can be nearly as useful in the overworld and in side-scrolling areas, as well. The tiles included are the duct ceiling (solid and see-through), inside corners, outside corners, duct walls, duct-to-wall tiles, and duct openings.

In screen two, the ceilings for the ducts are placed in the normal screen, the one the player will eventually walk into. Other than that, walkable dungeon edge overhead combos were used to connect two rooms via the duct. Note that I decided to make a smaller duct just for looks. It's basically the edges of the duct put together without the walkable area. This is good for nice ceiling effects, as well.

In screen three, this is what layer one of screen two looks like. These will go over screen two, with their respective wall combos working. This is basically the duct outline. This is my layer 1. Also, this is the layer to put in wall combos under the duct ceiling, just so the player won't be able to go up and down in the duct while going left or right. Basically, that invisible wall combo will have a wall for the upper part, and a floor for the lower part.

In screen four, it is screen three with many combos cut off. This is so the player will not end up under the duct while still being outside it. The still-existing combos are used to help cover the player as he travels through the duct, without him suddenly appearing through a duct wall. The reason I didn't delete the duct entrance tiles facing south was because it is okay for the player to be under those combos, since he'll be at the entrance.

Me, for creating the tiles.
Riyago, for being my test subject for those tiles.