[quigonkenny]

Way I see it, any transmutation that involves calling a soul "back" opens the Gate and takes a "toll". Ed and Al during the attempt to revive Tricia, (possibly) Ed again to bring back Al (although we didn't see it), and Izumi with her child. Also, if one knows how to open the Gate, they can open it under the right circumstances. Father and Hoho in Xerxes, Ed to get out of Gluttony, Pride and Mustang (using Goldtooth's knowledge) under Central, and of course Ed again to give up alchemy and get back Al. One's "first time", so to speak, may have to involve actual human transmutation and the toll (Father's body for Hoho, whatever Goldtooth became for Mustang, and Xerxian souls and Mustang's sight, respectively, for the tolls).

The pinning of souls to armor is a question mark for me. Chimeras (Tucker style) I can see avoiding the Gate, since it's a melding of things present, but soul affixing is real soul alchemy, manipulation of souls separate from the body, having much more in common with the kind of alchemy that got Izumi and the boys in all that trouble than anything else we've seen. It should open the Gate as well, you'd think. Of course, we don't know who actually affixed Barry and the Slicer brothers. It could have been Father, who had obviously already opened the Gate. It could have been Goldtooth, but usage of a Stone may preclude needing to open the gate (since the Stone pays the toll). Or it could have been some other nameless alchemist who either died during the attempt or later in one of the Human sacrifice "test runs" Father may have needed to perfect his plan...