So far I've counted about 20 baby mystery snails in my waterfall pond. Will they be able to winterover in there or should I pluck them out and put them in the big pond? The next 'step' is my 50 gal. skippy filter that the waterfall drops into, I was wondering if I should put them in there. They might be fish food if I put them in the big pond.

Apple snails (most "mystery snails" are apple snails) will die below about 50-55 degrees F so they need to come inside the house before then if the water gets cold where you live. If you live in a warm area, then I would just move them to your mini 50 gallon pond area and, when big enough, into the main pond. They can walk there themselves on rainy nights too. They may also wash down the waterfall if they lose their grip.

Guess I better hurry up and set up the aquarium in the puter room. I'll grab as many babies as I can. Fortunately Big Mama is bigger than a ping pong ball so I'll be able to grab her. ( 6ft. hubby spotted her in the 2ft. end..he was standing straight and she was on the bottom. lol--she's big!!) Neither of the two smaller ponds froze up last year..but no snails or fish. Plants were fine. Just not sure how cold the big pond will actually drop so better safe and sorry. I'll be still looking for Dude the pleco and still debating about the new feeder fry, since they're so small.
setting up plant pond in the basement for overwintering the floaters too.
thanks.