athass_prkr
aaaaaaaaaaaaaaa, author, if you think you're being smart by doing cliffhangers one by one, then that's stupid. This could work in some TV series, but not in a book, these are different types of storytelling, and what works for TV series (game of thrones) does not work for books. there are a lot of storylines in game of thrones, just like in your story, they also go at the same time, but there the series lasts an hour, and you have a chapter for 5 minutes of reading. It doesn't work, it's not interesting to wait 2-3 days when you release a chapter with the continuation of one of the story lines.
now I have two theories: 1) this Sirius and the smiling killer are the same and he is just acting to manipulate Neville on the order of Grindelwald so as to destroy Dumbledore's plan; 2) the smiling killer is part of the soul, an horcrux not fixed to an object but to a plane of existence that took with him the memory of the original Sirius (that we see here) and the memory of the original are just trying to repair themself by creating things to explain what happened.