I MADE MMF FOR THE 1ST TIME. I MUST SAY IT TASTED 100 MILLION % BETTER THAN WILTON. I MUST SAY THOUGH, I FOUNF IT HARD TO WORK WITH. UNLIKE THE WILTON STUFF, THE MMF WAS TOO STIFF AND DID NOT STRECH AT ALL, IT JUST BROKE/CRUMBLED APART. DID I DO SOMETHING WRONG OR IS THAT JUST THE NATURE OF IT?
I also just recently made MMF and love that taste of it. Sounds like you used too much powered sugar. The recipe I use is 1 bag mini marshmallows, 1 tablespoon water, microwave on high 1-2 minutes until puffed then stir into liquid. Pour this onto 1 pound confectioner sugar on a well greased surface knead and keep adding sugar until pliable if you get it too dry add Crisco. The chocolate MMF needed almost 2 pound sugar!? But it is very humid in Alabama! Hope this helps! 
I agree, it sounds like too much sugar. It mirrors my first attempted at MMF. Now I only add half the powdered sugar and then knead in small amounts of powdered sugar until I get the consistency I want.
You can also knead in some shortening to help give it stretch!
I MADE MMF FOR THE 1ST TIME. I MUST SAY IT TASTED 100 MILLION % BETTER THAN WILTON. I MUST SAY THOUGH, I FOUNF IT HARD TO WORK WITH. UNLIKE THE WILTON STUFF, THE MMF WAS TOO STIFF AND DID NOT STRECH AT ALL, IT JUST BROKE/CRUMBLED APART. DID I DO SOMETHING WRONG OR IS THAT JUST THE NATURE OF IT?
If you find that happening, add just a touch of liquid and/or Crisco, until it becomes pliable. As others have said, it means you added too much powdered sugar, but it is fixable. Don't add more than a teaspoon of liquid at a time, though! You can get a very sticky mess that way.
You can also knead in some shortening to help give it stretch! Corn syrup will do the same thing.
I have only made it twice, but the second time I did not use the full 2lb bag and it was much, much better. I also kneaded it for quite a long time. I let it rest in the fridge for a couple of days and then I needed to knead it again and get the consistency better.
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