The disappearing witch act is always a great way to start a story, it immediately sets the tone for an eerie adventure. I really like these mystery stories, the way Usagi and the Inspector over the game of Go felt like a classic detective parlor scene with a fun twist, and the misdirection with both the assistant Inspector and the Inspector was really fun to see play out.
One of the best parts of the story though takes place in the second part, the way Stan stretches out Usagi's walk through the town while being stalked by the demon mask with so many small panels gives you an almost claustrophobic feeling that puts you right in Usagi's shoes. But the master stroke of it all was the skull pattern on the demon mask's robes, it was subtle but fun.