My black mmf is to stretchy and tears when I lift it to cover my cake . I need advice ASAP ! TIA

Did you color it yourself? Unfortunately, for dark colors like black, blue, and red, you need to add so much coloring to it, it changes the consistency of the fondant. I usually make my own MMF and color it myself, but for those colors, I use store-bought. I don't really have any suggestions on what to do with that fondant, except maybe if you happen to have an airbrush machine, or even one of those spray colors, you can use grey fondant, then spray it black.

For my black MMF I use milk chocolate or dark chocolate instead of the white in my recipe This helps to give it a darker color with less black coloring added. This has worked really great for me. I also add the coloring in with the marshmallows just after I melted them. This has also helped. Sorry to say, but I dont see the batch you made being saved. You'll have to make a new batch. I hope this helps!