[@KatherinWinter]

The mask has always been connected to the Black Beast. I don't know why you keep thinking it has nothing to do with it.

Like I said, the Beast is looking for a face. And to the beast, a face is a [url=http://orig04.deviantart.net/b768/f/2012/068/6/3/skull_by_themanface-d4s781x.jpg]skull[/url]. So whenever Arachne wears a mask that looks like a skull (In this instance, a simple white mask with three holes, two being the eyes and one being the nose, is good enough), the Black Beast is drawn to it and takes it as it's face. The mask is symbolic to a skull, which is what the Black Beast wants. Thus, destroy what it wants drives the Black Beast back inside of Arachne.

Not only that but because Arachne still lacks control over the beast, even if the Black Beast is summoned for some other reason like that it's hungry, destroying the mask is good enough to drive the beast back into Arachne. Right now because Arachne doesn't have a good control over the Black Beast, she needs masks in order to summon it on her own. Later on once she gets stronger she can summon the Black Beast without masks, but that'll only happen after she accepts that the Black Beast is a part of her.

I based the Black Beast's hunger off the idea of Gluttony from the seven deadly sins. Most people think that gluttony just means eating a lot, but it goes deeper then that. It's the desire to have more than you really need, taking more than you deserve, and generally wanting something you shouldn't have. In this instance, Arachne bit off more than she could chew by staying in that forest despite all her friends leaving her. She challenged the cosmic forces because she wanted to do something interesting, despite how out-of-depth she really was. She wanted to show off and now she's paying the price for it. Now I know that also sounds like Greed, and those two are closely similar. But to me, Greed is more about not sharing what you have despite how much of it you do have. Gluttony takes more than it should, but Greed would never give what it can spare.

And yes, I will still continue to call it the Black Beast despite the fact it's a blob. It can turn into animals if it so desires, but being a blob is easier form for it to maintain since being a blob is it's natural form. Just like how shapeshifters tend to have a default form instead of staying a new form forever and ever.