so my mom is a big fan of novel writing and used to tell me that the best way to make a mystery novel was to start from the end and work your way forward, what do you think?
I say yes and no. It's a great idea to have the ending done, so the whole story moves in that direction. But I like to start with the start and then do the end, so you have both points nailed. Then you get the story going in the right way!
If you're writing a mystery, then you need to know what happened at the outset -- you need to know who did it, why, and how. As the "end" of the mystery involves answering all of those questions, then yes, you need to have the "end" in mind all along.
But that's not exactly the same as having a specific ending. There's a lot of room for variation as to exactly how you get to that reveal.
"VillainFest," going on right now, actually provides a pretty good illustration of this. One of the suggestions we make in approaching it is in being able to tell your story from the point of view of either the hero OR the villain. In a mystery, it's told from the hero's point of view, so you learn about the villain as he learns about it, but as a mystery writer, you should be able to tell the story from the point of view of the villain as he's trying to keep himself concealed from the hero, with you the reader knowing what the villain knows all along.
Fully develop both threads, the points of view of both characters, and you'll have a good place to start. Imagine the villain or antagonist as the man character trying to foil the hero or protagonist. Thoroughly know your villain and reveal that information in increments along the way.
But, if you have a very specific scene with very specific actions in mind for your last scene, you run more of a risk of your writing seeming contrived in order to get you to it.