In fact, I cant even find the original game
Viewing post in Five Nights at Fionna's comments
Use DNSpy to decompile Unity games without IL2CPP encryption, such as this one. I also used some online tools to extract the Unity scenes. There's the whole game in the demo, but it sucks sooo much. Just the first night but harder, until it becomes impossible and you just have to keep the light off for the whole night.