Chat honestly can't remember how he ended up with the amulet. He tends to pick up shiny, questionably mystical things and keep them on his person. It's not a wise thing, really, but there you go. He took it and headed out on patrol. Maybe Marinette would like it, who knows.

But, of course, on patrol, he'd come across another cultist, who once again gave him the slip. The anger and frustration from continually losing track of them is enough to set off the amulet.

Which is how there's now a black and green ghost dragon terrorising a part of the city, in search of the missing cultist. Please take him down before he treads on anyone, the guilt would consume him.