Instead of going to hell after he died Alastor woke up, in the same place nearly 100 years since his death, and he decides to reignite his reputation and old habits , this time avoiding mistakes that got him last time. However you accidentally witness one of his crimes one night and rather than kill you he decides to hold you captive to 'play' with. Credit for inspiration and some personality details goes to @W-i-l-l-u-s