The character that changed the most would have to be "Wolf". He made Scarlet fall in love with him as he fell in love with her, then betrayed her only to fall back in love with her. He was forced to betray her becuase he was part of a pack with Lunars and "wolves". If he did back out he would've been killed by them.
The ending was deeply romantic and very adventurous leading up to a good cliff-hanger. I espeacially loved the character Cinder who came back from the first book to try and defeat the evil Lunar Queen, Levana, that is trying to kill Emperor Kaito.
This movie also reminds me of "The Princess Bride".
This is a clip of wolves howling. :)