I thought I should write this just in case someone didn't understand what Pitch meant by 'fallen beast' in Chapter 9 Part 1
Also has some info on Crystal's past that makes her the girl she is now.
Crystal is shy and usually keeps to herself. She is very kind-hearted and 'pure.' She grew older and ended her 'stupid naive logic.' She started fitting her 'puzzles'(memories) together and all the bad things popped out even more than her pleasant ones. Crystal is naturally pessimistic. She started to get bullied and spiraled into an unnoticeable depression. People never expected her to be so sad because she always smiled.
No one was close to her. When she had friends, she kept them at a distance where she was not at their reach.
So! When Crystal was crying, Pitch came. He took an interest in her, and somehow, she just made him melt. Crystal was the only person that Pitch never tried to hurt. She was vulnerable, emotionally sensitive, and moving. Pitch felt that she was familiar to a very far off memory. Meaning, his memories of his human life is blurry and Crystal was actually like his daughter. She was gentle and had almost been a complete match to Pitch's beloved daughter.
When Pitch mentioned Crystal as a 'fallen beast,' he only saw her being bullied and being a broken angel. The reason her wings were bloody was all those pain that she felt. Her broken wing resembled her broken self when she was being bullied. Crystal cried alone so there was no one to help aid her wings since Pitch went to bring Nightmares to forgotten South American towns. Pitch forgot all about her and never came back. Crystal kept getting worst until she stopped listening to anything around her, thinking it would cause more pain. That's when she developed Borderline Personality Disorder. Remember! Her parents also tried taking her life away!
Crystal could never escape her past, that is, until she finally opened her eyes to see that she had her siblings, Jack, Pitch, and the rest of the Guardians. They all cared for her, and she finally felt it was real. Thus, her wing healed and the blood was washed away to indicate that she was now a real angel. Pure, innocent, and strong willed.