Hi, the.blue.bunny!
Sorry you are running into this. UnityPlayer.dll is necessary to run the game as it contains the code for the engine we use and is bundled with the zip of the game. I just double checked to be sure, and the windows downloads (both the 32 bit and 64 bit versions) have the dll at the root of the zip file. Can you check whether the UnityPlayer.dll is still beside the morticianstale.exe file wherever you have it extracted?
If you've extracted everything but the dll is missing, something may be moving or deleting it. You'll need the correct version of the dll for the game to run, so taking the dll from another source likely won't work (and I would strongly recommend not using any UnityPlayer.dll files you may find on the internet as they may be malicious).
Do you have antivirus software running? It's possible that it is quarantining the file when it gets extracted.
- Andrew