I attempted to make MMF for the first time and it didnt turn out.

I am going to try again and wondered. If I am adding a flavoring, do i add it in addition to the water or replace part/all of the water? Thanks.

Yes, for instance, if you want to add 1 tsp of flavoring, you should decrease the water by 1 tsp.

Here's the recipe I use. It always comes out perfectly for me:

1- 16 oz bag of mini marshmallows
1 1/2 tbsp water
1/2 tbsp clear vanilla extract
7 cups powdered sugar (2 pound bag MINUS 1 cup)