This has been going on for a while, and I don't know how Entropy feels about it, but I really don't think there's a need to ask for answers from one of us. There are other competent people around. Other people who have located the "Rules questions" link.
About Arcane Power: Apparently, this has been difficult for some people, I've been asked about it by others too. Yes, there's no "…". That doesn't mean the text in the errata is supposed to be the full card text. Because then it wouldn't even be an "Action:", that's not in the errata text either. It would be a Tactic with a constant effect, that doesn't make any sense. They forgot to print the "…", probably because it was just a change to the previous errata. The errata for The Unending Horde is missing the "…" at the start too, but no one seems to think you can't attach units to it anymore.
So, Arcane Power should be read as
Action: Draw a card. Then, if you control a legend or Artefact support card, return target card (other than an Arcane Power) from your discard pile to your hand.
Brad has confirmed this.