The Beast Cutter is one of the first weapons you’ll be able to find early on in Bloodborne: The Old Hunters. Assuming you’ve already unlocked the first shortcut from the Hunter’s Nightmare lamp, run up the steps, past the hunter, and into the area with all the steps leading up to the Grand Cathedral where you face Vicar Amelia (or a different boss if you’ve got the right item in this DLC). Go up to the platform on the left side and take a short drop down to where the 3 man-beasts are.
However, watch out for the blood-addled hunter that’s waiting for you just past the man-beasts. If you can run past him, you’ll be able to grab the item sitting on the ledge right behind him. That’s the Beast Cutter you’re looking for.
“A trick weapon used by Old Hunters.
This thick iron cleaver slices through the toughest of beast, and when transformed the blade splits into sections, allowing one to lash it in the fashion of a heavy whip.
This crude weapon relies on brute force and is regrettably inelegant, suggesting that the hunts of the earliest hunters made for horrific affairs, painted in sanguine black and reds.”