Melt the milk chocolate melting wafers in a microwave safe bowl in 30 second intervals, stirring well between each interval, until smooth.
Spoon a small amount of melted chocolate into each cavity of your silicone ghost mold. Use the back of a spoon or a small brush to spread the chocolate evenly along the bottom and sides of each cavity, making sure the entire shape is well coated. Allow the chocolate to harden, about 10 minutes. If you'd like you can put them in the refrigerator for 10 minutes.
While the chocolate is setting, add the peanut butter, melted butter, vanilla extract, light brown sugar, powdered sugar, and kosher salt to a medium sized bowl. Mix until smooth and thick.
Gently press the peanut butter filling into each chocolate lined ghost cavity, leaving a little space at the top for the final layer of chocolate. Flatten the filling so the tops are as even as possible. Spoon additional melted milk chocolate over the peanut butter filling to completely seal each ghost. Smooth the chocolate across the top.
Let set for about 30 minutes, or until completely firm. Once set, gently flex the silicone mold away from each ghost and carefully pop them out. Enjoy immediately or store in an airtight container.