Instructions
Play a local multiplayer or an Internet multiplayer game of "Castlevania HD" with at least two players.
Choose to play as Jonathan Morris at the character selection screen. It doesn't matter who the second player chooses.
Select the "Hard" difficulty level, as it gives you the highest chance of getting "Jonathan's Bible" on the first try. It is possible to get this rare item on the "Normal" setting, but it may require several tries.
Play through all of Chapter One and begin Chapter Two: Lord of Unseen Strings.
Play through Chapter Two until you reach the boss battle with the Puppetmaster. This boss can be tricky, as it will summon an iron maiden and try to trap you and your partner inside for significant damage. If either of you has less than 160 HP when you're trapped inside, you will probably die from the attack.
Keep Jonathan between the Puppetmaster and his iron maiden and use the wrecking ball attack. This will hit the boss and his puppets twice per rotation, all while keeping you out of harm's way. A well-timed forward roll can also help you avoid the Puppetmaster's attacks. Continue your attacks until the Puppetmaster is defeated.
Collect the item from the chest that the Puppetmaster leaves behind. It is likely to be "Jonathan's Bible."
Continue into the room on the right. This room will have three fire traps and three weighted switches. Enter the room on the top while your partner enters on the bottom. Have your partner stand on the switch on the lower right side of the room. This will allow you to cross over to the purple chest.
Open the purple chest. This chest can also contain "Jonathan's Bible."
Restart Chapter Two and repeat the process if you didn't get "Jonathan's Bible" on the first try. There is a good chance that you'll get the weapon, but it is not guaranteed.