In every chapter of the Wolf Among Us there are trophies for unlocking all the fables, there are missable ones that you will need to rewind the chapter in order to obtain.
Missable Fable Location:
To get the final entry you simply need to rewind to the last part of the final “Chapter 6: A Light Snowfall” to replay it, and either:
1) Choose “Wolf’s Rage” to rip off Grendel’s arm, or
2) Instead choose “Wolf’s Mercy” to leave it and walk away.
Just do the opposite to what you did the first time around.