This game saves data in the registry under the following key:

HKEY_CURRENT_USER\Software\ZigZag Soft\FerrumSecrets

You can export the key by right clicking on it if you need to make saves. I highly recommend it when playing in expert mode, just in case something goes wrong.

It's possible that the gloves needed to go down the rope to enter Arthur's room in the factory become glitched. It becomes impossible to drag them on the rope. After a few tries I tried just clicking on the gloves and then on the entrance to Arthur's room and it worked. Luck? You tell me.

The game can troll you right before you complete it by failing to detect that the explosives have been placed. When trying to board the plane it'll tell you that you need to plant the explosives, yet you already did it and can't change anything. Oops. This happened to me when going to the menu after putting the explosives. When I was back, they were gone from both my inventory and the rest of the game.

This can be fixed with some registry editing that reenables the location where you put the bomb and puts the bomb back into your inventory.

Run > regedit.exe

There go to the key HKEY_CURRENT_USER\Software\ZigZag Soft\FerrumSecrets

Double click on _itemSteamFactory_enabled_collider_h1977236614 and set the value to 1

Then do Edit > New > Binary Value, name the key _item2_h3488964477 and set the value to 69 74 65 6d 42 6f 6d 62 00

Load the game, continue, go put the bomb again and go back to your plane. Enjoy!

There are a couple tricks to expert mode, other than regularly saving the game by exporting the registry (then importing back if you need to load it, before clicking continue in the menu). If you reload the game to a point before you pick a collector's item, be sure to pick it up again!

The timer will not move during cutscenes. It will however move during dialogs that can be advanced by pressing Space. Be careful.

The timer will not move during puzzles. Take your time, and look up what you have to do next.

The timer will reset if you go to the menu and resume the game. This makes some of the harder segments of the game trivial, especially those involving collector items as those do not reset the timer.

In the basement you can use the light object from the first room to reset the timer. But going into the menu and back works just as well.

This game is very buggy so there's probably more bugs. You can try fixing them by editing the registry, only took me an hour to figure out the fix for the bomb... Yeah. At least the achievements are not bugged. Hope you won't run into too many issues. Enjoy!