Serial Cleaner DLC Blood and Confetti is officially out now bringing more content to the 2D action-stealth game.
The game has you cleaning up crime scenes so the cops don't have any evidence. It's a great with a Native Linux version. I had completed all the main missions back a while ago and I decided to finish all the movie missions before the new DLC.
After the DLC dropped, I picked it up and started the game. I didn't see any new missions. Uninstalling and reinstalling didn't help. Looking at YouTube videos showed a new intro and new menu option.
Then when enabling Proton compatibility, I installed the Windows version of the game. Behold the new intro and menu. I can't play any of the old missions or movie missions since my save file didn't have my progress. I tried copying the Linux save file to the Windows location but that didn't work. The old save files files seem to have been compressed while the new ones are simply json.
Looking on the forums, I discovered I wouldn't have fared any better if I had played the Windows version originally. Seems Windows players lost all their progress because the updated game couldn't read the old saves. They did add in a hack that if you get the Mommy's Little Boy achievement it unlocks all the missions. As the save files are json you could just edit the files as well.
Why did this happen? The DLC was delayed from it's initial release date. The developer admitted that after 8 years only two of the original developers remained. They had to relearn the code and also upgraded it to new version of Unity. The sequel game didn't support Linux so I suspect the team member(s) who implemented Linux support left. On Steam they said "It's not coming in the near future. We want to do it, but have no solid plan at this moment" about an updated Linux version with DLC support. So for now, you'll need Proton.
The DLC is only three maps and doesn't add any new mechanics but I've enjoyed it. I love returning to games with new levels even if nothing else changes. If you are not that type of person, you should look at the sequel game instead called Serial Cleaners. I haven't gotten very far in the sequel but I have already seen several new features and have been enjoying it too.