Stir boiling water into dry gelatin in medium bowl at least 2 minutes until completely dissolved. Stir in cold water.
Let stand 20 minutes to cool.
Add ice cream; stir until completely melted. Stir in 1-1/2 cups of the marshmallows. (They will float to the top.) Spray 5-cup bunny mold or other shaped mold on tray; spray with cooking spray.
Pour gelatin mixture into prepared mold.
Refrigerate 4 hours or until firm. Unmold onto serving plate.
Garnish with remaining marshmallows. Store leftover gelatin mold in refrigerator.