Gremlins 2: The New Batch -

This is the most critical rule. Eating after midnight triggers the cocooning process that turns a Mogwai into a Gremlin. 2. A "Civilized" Survival Guide

Thanks to the Splice o' Life lab, be prepared for Gremlins that can fly, talk, or even turn into electricity. Gremlins 2: The New Batch

Don't get them wet. One drop of water creates a "New Batch" of Mogwai. This is the most critical rule