Preheat the oven to 250 degrees Fahrenheit and line a baking sheet with parchment paper. Draw four ghost outlines on the paper as a guide.
In a clean bowl, beat the egg whites on medium speed until soft peaks form. Gradually add the granulated sugar while beating on high until stiff, glossy peaks develop.
Gently fold in the cornstarch and vanilla extract until just combined. Spoon or pipe the meringue onto the parchment in ghost shapes, creating raised peaks for the heads and bodies.
Bake for 90 minutes, then turn off the oven and leave the meringues inside to cool completely without opening the door.
In a separate bowl, whip the heavy whipping cream with the powdered sugar until soft peaks form. Keep the cream chilled until assembly.
Place the cooled meringue ghosts on plates. Spoon the whipped cream over each one and scatter the mixed berries on top and around the base.