Egg whites form a spooky, frothy top, giving the cocktail a mad-scientist makeover. The cocktail gets its green hue from Midori liqueur, a super sweet muskmelon-flavored liqueur. Serve in beakers or test tubes to up the Halloween aura.
Combine gin, lemon juice, midori, and egg whites in a cocktail shaker filled with ice. Shake vigorously for 1 to 2 minutes. Strain into glasses. Spoon foam onto drink, if desired.