Place the white chocolate pieces in a microwave-safe bowl and heat in 30-second bursts, stirring after each, until fully melted and smooth.
Spread the melted white chocolate in a thin, even layer across a serving board or a sheet of parchment paper set on the board.
While the chocolate is still soft, press the mini marshmallows into it in small clusters to form ghost shapes.
Add the candy eyes to the tops of the marshmallows to finish the ghosts.
Scatter the strawberries, raspberries, blueberries, and blackberries around the chocolate and marshmallows, leaving some white chocolate visible between the fruit.