how. the. fuck. am i supposed to get it  

You must meet Witer's quest first about his nightmare

Wait until its Day 7 then keep on talking to Wilter and After you talked to him 3 times ask the Tavern Members (You need to unlock the Basement for the Ghost Horn) Then talk to him and wait until 3:00 - 3:55 am and talk to Wilter in the Basement

Ummm a question can i still get the fist on day 66? Asking for a friend 😭😂