Cult of the Lamb

This achievement is practically story related with this DLC. When going back through Darkwood, the first area, you will unavoidably come to a room where you'll meet Midas. He will steal a huge amount of your Gold and then disappear. Later, when you access Anchordeep, the third area, and work your way through it, you will once again unavoidably come to a room with Midas, and he will again still most of your Gold. Finally, once you work your way through Silk Cradle, the final area, you'll find Midas for the third and final time. Once you find him, you now need to attack him over and over. He'll drop Gold (although it's a pathetic amount compared to how much he likely stole from you) for a while, so you'll need to hit him probably around ten times. Once he stops dropping gold and looks all beat up, this achievement will unlock. It actually had around a ten second delay for me, so just be aware of that.