In a medium bowl, combine cream cheese, brown sugar, caramel topping and vanilla. Beat with an electric hand-mixer until smooth. Add the 1 cup marshmallow fluff and beat on low speed until combined.
Cut apples into slices. In a small bowl, combine lemon juice and water. Toss apple slices into the lemon juice mixture. (This will prevent apples from turning brown quickly) Drain.
Serve by dipping apple slices into dip. Enjoy!