Credit goes to Ryuu on Steam for pointing me in the right direction.

Credit goes to /u/GMMan_BZFlag for writing the guide on Reddit.

Credit to InsertCookiesHere for confirming versions.

All the information was pulled from here:
https://www.reddit.com/r/Steam/comments/611h5e/guide_how_to_download_older_versions_of_a_game_on/

If I made any mistakes, let me know in the comments.

Basically what you want to do is open up the Steam Console: steam://nav/console

I'm having problems with Steam formatting here, when I test the link Steam claims that the link may be malicious, but it is not; so enter into your browser and it should open this:



Click Open Link and it will open up the console in your Steam Client.

Enter into the console:

For version 1.5.13:
For version 1.6.7:
It will download the old depo and tell you the location it is saved to once it is complete. Back that folder up into a safe location (you can rename it).

Copy the contents of that folder directly into your FTL folder, and then launch FTL the same way you always have. Enjoy the old version of FTL!

You can find FTL's folder by right clicking FTL in your games list, select "properties", go to the "Local Files" tab, and select "Browse Local Files..."



If the game ever updates, just copy the contents of the depo download back into the FTL folder again.

This is what your FTL will look like again (1.5.13):

Version 1.5.13

open: steam://nav/console
enter: download_depot 212680 212681 3032798599689269105
Copy contents into FTL folder.
Play through Steam!

Version 1.6.7

open: steam://nav/console
enter: download_depot 212680 212681 928569786008768839
Copy contents into FTL folder.
Play through Steam!

Enter in:

Version 1.5.13

Version 1.6.7

Thanks to oKruszek for confirming it works.

For Version 1.5.13

For Version 1.6.7