I am not sure if it is all that difficult to accomplish a guppy x molly hybrid. When I was faily new to fish I actually had my fancy guppy get my silver molly pregnant The result was my silver molly giving birth to 70some-odd very blotchy fish some having grey patches on white, all white, and white patches on grey. From what I remember that was an unusualy large number of fish for my molly to have to at one time. Maybe due to the smally fry size of the guppy? Anyway, I removed them from the 10 gallon I was keeping them in and put them in a margarine container in hope of preventing the mother from eating them. After a few days they died. If you are really interested in creating this hybrid I'd suggest breeding a male guppy with a female molly. The only reason for this is that i obersved that my male guppy (aka "the horny fish") would try to mate with practically any fish in my tank, even other males and am not too sure if a molly would do the same. Personally, I think my female molly was avoiding him as best she could and that the cross wouldn't happen in the wild.