The demo is now playable in Steam. Go play it!
The version consists of the early parts of the game. Most unlockable content is restricted, but saves are shared between the release version of the game. You can access the content you have unlocked later in the main game.
The game may be tough. Demo will be actively updated and balanced in the coming weeks.
Hope you enjoy it!
https://store.steampowered.com/app/2775280/Dead_Underworld_Demo/