Got stuck because you couldn’t get the Lunarium Key? Good news! The new patch is supposed to fix that.
Apparently, the key became unobtainable once players joined an online multiplayer game in the Forbidden Woods.

Don’t ask me about any of this. I’m still stuck at the first boss and since they also fixed an exploit that allowed you to duplicate certain items, it looks like I will be so for quite some time.
Let’s get back to Nintendo now, before I break into tears.

Source: Videogamer.com