From the noobtorial thread:
By PixelSnader:

The correct way to build ground shadows is relatively easy though.
Just draw lines, and see where they hit the ground. Here's an example:

1 - original WIP image
2 - raycasting a bunch of key points
3 - correct shadow
4 - you can try to tweak a bit to get cleaner lines and more detail. for example, the overhang of the roof.

Edit: I used a simple 1:1 step because it's easy, but you can see that it makes the shadow a bit wid/big. If you want to save tile space or something, you might want to try a 1:2 step to get a much smaller shadow.

wip for 43

wip 43 update
Added one more tentacle ans some other colors from palette.
Do I have to draw shadow of the tentacle in the upper corner?

Some are saying that the reason for the calamity was a failure in communication systems.
WIP.

Okay... So can I take tile #26 now?

41 is mine

You can only take tiles with a complete neighbor now. 69, 84 and 85 are best candidates.

I think some parts of this tile need to be fixed. However, there is nothing more I could do myself, so, I guess 43 is done.

Calling it done.

Thanks, Irenaart.

Those outlines are very bold for this collab. Maybe consider making them brighter and harder to notice?

more wip on #40, just need a few more tweaks before I call it done.

edit:

#40 is done

43
Fixed outlines. Now, certainly done.

Hello, I'd like to particpate. I'll take any tile that's neighbouring a completed tile.

I was waiting so much for #11 to be done, since @Dont claimed #4, I want #3, please.

Maybe do something along the lines of "eeny meeny miny moe" with your possible tile number choices? Or you can maybe toss them into a list randomizer and pick the number that the randomizer selected as number 1 :)

I'm not sure what else to add to the tile (apart from maybe cracks in the road). Any suggestions?

#85
SSS

@all, its cool to update even after you call it finished :)

WIP 39

May I reserve #48. I know that #41 will give key elements for that part, and I'll wait for it. But this tile intrigues me... 

Main image and reservations updated.

@dont, drain, irenaart; tiles are yours.

@Axoloth; 19 is diagonally neigbor to your own tile, can you pick another?

@metaru & magpie; you can pick any available tiles but the ones I suggest are: 69, 78, 92 and 93.

@Duckpsycho; your objects lack volume. I will give you some detailed advice but don't have any time on weekends :/

done!

28 is done.

can I have tile 20? nah, jokes aside, what about tile 69?

wait, outer tiles don't need to match each other? (#3 and #4)

Calling it done. I still need to add people in the little shelter but too lazy to do rn