Really need this question answered. So, define moving THROUGH. Can torodin move onto a unit and then BACK where he came from to wound? Can he wound when a unit is against the wall, that is, the edge of the map?
I can't find a definitive answer to your question, but the folks over on the Summoner Wars forum seem to agree that it is legal to move onto an opponent and back to your original space.
Note that if you use the "Torodin's Advance" event card to increase his movement distance, any units you trample receive a maximum of one wound marker each (even if you were to move on and off of one of them two times).