Rare Replay

You should get this naturally as you play through the game.
If you want to speed things up go to challenges and press

On this screen you can see which books you need, go down the list and load up Chapter 2, Scene 5: Conservatory

After defeating the enemies in the room and opening the door, one enemy will drop into the room, kill it and another one will drop down, so you can pound out your remaining kills one at a time.

From the main menu, go to bonus challenges and select the 1st one Billiard Room Bust-up!

This simply involves killing as many skeletons in 60 seconds as possible. You should be averaging between 10 and 20 every time.

Try to use the 3 billiard cues in the corner and spin the billiard table when a large group is near for maximum damage.

It will still take a while but for me was the quickest way.

side note: You may have to unlock this challenge by playing a little of the main story, I didn't try until after chapter 2.

Hope this helps