Add sugar, cornstarch and milk to a large saucepan over medium heat and mix until smooth. Stir constantly until it begins to thicken. Reduce heat and continue to cook for about 2 minutes.
Remove from heat and add about 1 tablespoon of milk mixture to eggs, whisking until smooth. Slowly add 2 more tablespoons and pour egg mixture back into saucepan. Return to medium heat and bring to a boil, stirring until mixture thickens, about 2 minutes.
Remove from heat and add butter and vanilla and transfer to a bowl. Place plastic wrap directly onto the custard and place in fridge to chill.
Preheat oil in a Dutch oven to 350 degrees.
Open biscuit dough and separate all of the biscuit rounds into 2 pieces. Cut half of the rounds in half. Add a fingertip of water to the tops of the rounds and stick on the halves. Use a knife to score a thin line at the bottom of the dough half. Use remaining dough to roll out into thin strips.
Add dough to hot oil, working in batches until golden, and set aside on a cooling rack. Add dough strips and fry until golden and remove to cooling rack.
Add custard to a piping bag and pipe into fried donuts. Dip the tips of the donuts into melted chocolate. Stretch caramel into thin strips and stick on the back of the donuts. Using a small paint brush, paint food coloring stripes in between caramel. Stick fried strips into donuts, making legs and antennas.