I'm a hobbyist who uses marshmallow fondant because that's all I can afford. This past week my sister and I were working on a cake for my mother's birthday. Because my sister had a particularly difficult and busy week (moving, working, taking care of her infant), most of the work on the cake fell to myself. My sister had a little bit of leftover fondant from a cake she'd made recently so she gave it to me. I also had a little bit of leftover fondant, but whereas her fondant was nice and stretchy, mine was spongy. My fondant is ALWAYS spongy, never stretchy.

I tried to make my next batch of fondant according to my sister's instructions, but it was still spongy! Additionally, it always gets quite a few air bubbles when I roll it out, and when rolled out on crisco, comes away covered in pockmarks. My sister said she rolls hers out on crisco and she never gets pockmarks. What's my problem?

MMF tastes better, nevermind it being cheaper!
Hmmmm....spongy sound like you have too much PS in your fondant. Try adding less to start, and SLOWLY adding more as needed.....my recipe calls for 2lbs but I have never used that much in mine.
I also only use Crisco when I am first kneading it. When I am getting it ready for a cake, I roll it out on CS. HTH

I am struggling with the same problem... Sometimes my MMF turns out perfect, and then at other it doesn't roll out right and tears easily. Had a batch turn out horrible yesterday, and the only thing I can figure I did different was I used store brand marshmallows instead of Jet-Puffed marshmallow... I'm starting to think the problem might be due to cheap marshmallows. I'm going to do another batch today with the JetPuffed and see how it turns out.

I use cheap marshmallows every time (Kroger, Publix, Target, or Walmart brands) and have never had a problem. Sometimes if the marshmallows aren't fresh you might have a problem.

What recipe are you using?

16 oz. marshmallows melted with 2 tbsp. water (2 1/2 min., stirring every 30 sec.). The recipe calls for 2 lbs. PS. Once melted, I coat my counter liberally with Crisco, then put about 1 lb of PS on top of that, then i pour the marshmallows on top, and put maybe 1/2 lbs more of PS on top. Then I start kneading. I look for a nice stretchiness. That's usually all I need, but I would rather have it need more than have to try to rescue it once it has gone too far (because I have no success with the rescue efforts, and usually end up throwing it away, lol). Sometime I don't even use all of the PS on the counter. I let it rest at least 15 minutes, then come back to it, and if it needs more PS, I add it in while I'm adding my color in.

Hmm, I tried adding less powdered sugar this last time -- and added it in very gradually -- only stopping once the stuff was no longer very sticky. Should I just let it stay sticky? I'm getting tired of the stuff I keep coming up with and am considering just giving up altogether!

Mine is always just barely past sticky, and the second it gets like that I tap it lightly in the PS on the counter, and put it in a Ziploc, let it sit for at leat 15 minutes (usually ends up being 30 or more because of the little one, lol). I clean my counter and dust it CS. Then I put the fondant down, add my color, and it's still sticky, and I slowly add more PS, adding more color/PS as needed and get it to the perfect color/consistency. I keep my couter dusted with CS when I roll it out. It rolls out easily on CS and doesn't get absorbed like PS. HTH....

I used mmf to cover the cake board for my class and I noticed there's bubbles and pockmarks. And then I used Virgin Ice to cover my cake - no bubble nor pockmarks. I really want to use mmf cos it is cheaper...but now I am in a dilemma about the quality and appearance.

I also have good and bad days with my MMF!! It's so frustrating, especially with the amount of waste you have if you have to throw it away.  I notice that on my good days, I'm taking my time adding the PS.  I never end up using as much as the recipe calls for. If too much is added and I'm not paying attention, I definitely end up with a non-maleable, spongy, pocked, useless fondant.  I almost had that happen yesterday while finishing a cake, and I was low on PS so I HAD to make it work! Luckily it was okay.