it seems that he has a broken bone? he cant move his tail at all. and the fish ( other mollys) look like their eating something off of him? did he brake his back?will he survive? ( i think no...) ;(

try to feel the bones to see if you feel cracks, or if your dog reacts at all. did you also try doing something to excite him? try doing that to see if his tail can wag. if you still don't know what's wrong, go to the vet.

Well o think your fishes are eating him mainly and your molly did break a bone but it should still be able to live and swim I'd you could some how keep it in your tank but don't let the other fishes hurt it and watch how it is day by day and take special care of it but it might be stuck with a bent tail for the rest or it's life because I have seen female guppies and a pleco or two that did just fine with broken tails

There's no way to know with only the information you've given us. However, if the fish is suffering and you expect no recovery, you should euthanize this fish.

The best thing to do right now is isolate him. Get a breeding net box to put him in. http://www.petco.com/product/13623/Penn-… That way he wont be stressed out by the other fish. He will be left in peace. If his body will heal, that will help him do it. I don’t know what else to tell you without seeing the fish. Good luck to you and your Molly.