How to layer images and create alpha transparency? I've created two node maps (or whatever they're called), one of which layers image textures on top of each other...


And another which allows the transparent parts of the images to be properly rendered...


But, when I try to combine the two, I notice something's missing.  Specifically, I don't know what to plug in to the "Fac" slot on the Mix Shader.


I've tried connecting everything from every other node, but it either screws up what I've already done (for example, certain textures disappearing) or does nothing.  I'm pretty new to this, so I have no idea what I should do.  In fact, the node maps were taken from some tutorials I found.  Any help would be appreciated.
Good news!  I managed to figure it out.  I found this thread here, recreated the node map in the last picture on that thread, and lowered the emission strength so the villager wasn't blindingly bright.

Edit: Turns out replacing the Emission node with a Diffuse BSDF node works as well.  Good to know.