Nice I like your style of writing. It has a good amount of background detail, although It can be more interesting if you can add more depth to your details such as a feeling before "DARKNESS". Was something going through his mind or something. And for the "black things" attacking as we can obviously refer to as heartless, did Mark have a strange feeling before they appeared and how did they appear. Idk this is just my thoughts. Don't get me wrong, I like your story so far and I'm not forcing you to change it. Just some thoughtful criticism. Can't wait to see more.