Mix 1/2 cup of the water with the gelatin in a large mixing bowl. Let sit for 10 minutes, allowing to bloom.
In a small saucepan over medium heat, mix the other 1/2 cup of water and sugar and bring to a low boil. Allow sugar to dissolve completely and remove from heat.
Add vanilla extra to water/gelatin mixture. Turn on mixer to low setting and slowly add in sugar/water mixture.
Mix on low for two minutes until fully combined. Increase speed to high for 5-8 minutes until a marshmallow consistency forms.
Melt butter on low heat in a large pot. Add prepared marshmallow batter and stir. Remove heat. Slowly add in Rice Krispies cereal while stirring continuously.
Once mixed completely, spread mixture into greased casserole dish.
Allow treats to sit for about 15-20 minutes. Before the Krispies have completely set, scoop out some of the Krispies and use your hands to mold into the shape of a head. Scoop out a smaller bit for ears and a nose. Place candy eyeballs, and add colored icing for hair.
Trim down disposable mask to about a third it's size (or small enough to fit your Krispie head) and reattach elastic loops with tape.