Besides planeswalkers, there are a lot of other cards that Hammer matches up favorably against, which is a lot of what the new era of Magic is about (that whole "subgame" thing again)
Having multiple Orb of Origins on the battlefield will have no additional effect on artifacts on the battlefield except that the Orb of Origins will also make each other mono and continuous
It takes a hit on the ranking due to how hard it is to get the planeswalker on board in the first place
If youre comfortable with Scryfalls custom search syntax, youll have your answer in seconds
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Unlike Cockatrice, though, Octgn is only available for Windows