In a small mixing bowl add unflavored gelatin powder. Add 1 cup of cold water. Soak the gelatin for 2 minutes. Whisk until dissolved.
Add 1 cup of hot water and grape Jello to the bowl. Whisk until everything is dissolved.
Add sparkling grape juice. Whisk to combine.
Spray pan with cooking spray oil and wipe. This will leave just enough oil to keep the Jello from sticking to the pan. Pour Jello into pan and place in the fridge for about an hour, or until very firm.
Take a knife and gently go around the edges of the Jello. Place a large plate or cutting board on top of the pan and flip over and lift up the pan. The Jello should slide right out of the pan. Cut the Jello into squares with a large knife.
Garnish with colored sugar and/or sprinkles and mermaid tails if desired.