Prepare a 13 in. by 9 in. pan with vegetable pan spray and dust with confectioners' sugar.
In large mixing bowl, sprinkle gelatin over 1/2 cup pumpkin ale.
In large saucepan, combine granulated sugar, corn syrup, and 1/2 cup ale. Bring to a boil over medium heat, stirring until sugar dissolves. Using a candy thermometer, boil until mixture reaches 240°F; do not stir mixture. Immediately pour mixture over softened gelatin; stir until dissolved. Whip on high speed until mixture triples in volume, about 8 to 10 minutes.
In medium bowl, whisk meringue powder and remaining 1/4 cup ale until foamy and thickened slightly. Add to gelatin mixture with vanilla and salt, and whip until thoroughly combined. Pour into prepared pan. Refrigerate until firm, at least 4 hours.
Spray a knife with vegetable pan spray and cut marshmallows into 24 squares. Toss with confectioners' sugar until lightly coated, dusting off excess. Drizzle with melted chocolate; let sit until chocolate has hardened. Store in airtight container at room temperature.
Note: To flatten beer, pour into an open container (such as a measuring cup) and refrigerate overnight.