Preheat the oven to 350°F and line a small square baking pan with parchment. Melt the butter in a bowl, then stir in 3/4 cup sugar until combined.
Add the eggs one at a time, mixing well after each. Stir in the black cocoa powder, flour, and salt until the batter is smooth and dark.
Spread the batter evenly in the pan and bake for 20 minutes. Remove and let the brownies cool completely in the pan.
Once cooled, beat the egg whites with an electric mixer until foamy. Gradually add 1/4 cup sugar and the vanilla, then continue beating until stiff peaks form.
Spoon the meringue into a piping bag and pipe ghost shapes on top of the brownies. Press candy eyes into each ghost.
Return the pan to the oven for 5 minutes to set the meringue lightly, then remove and let cool before slicing.