Bloodborne has a nasty glitch that will let you duplicate all in-game consumables.
The glitch was discovered by Kotaku and makes item duplication pretty simple.
Note that doing this will trivialise a major part of the game’s challenge and that it will probably get patched soon.
For this glitch to work, you’ll need to create an alternate character and play until you could warp to the Hunter’s Dream. Once that’s done, go back your main character and empty the chest in the Hunter’s Dream of all items. Go back to your alternate character and buy a pebble, then store said pebble in the chest – provided it’s the only thing stored there.
Now switch back to the main character, decide what you want to dupe and put one of it in the chest. After you do that, go and buy a lot of pebbles, depending on how much you want to duplicate. As always, items that are more than you can carry will go to the chest.
This short video demonstrates this tricky bit:
For other, more solid tactics, check out our Bloodborne guide.