Oh, so much good stuff! I am, as a mother, vindictively pleased that Harry felt so awful after the cigarettes. But how right you are that he would go ahead and give them a go.
Snape saving Dora from the pixies was full of tension, Sirius and Remus talking about electives was cute, and the snake in the forest was deeply creepy. I shall have nightmares about the spiders - urrrgh.

Definitely stellar work.