The arena was a really cool addition to the game, but it only lets players face off versus the ai. What could be a cool idea would be to add a way for players to pit their own AI controlled arena decks against those of other players. The player would get to watch the battle as a spectator...
Even cooler would be to allow multiple players to view the fight at once (maybe as an option under spectator mode). Or better yet, allow players to gamble electrum on the winner. It could make for some very cool tournament fun.
Finally, having an option to make a video of a match would be very cool as well. Maybe elements could one day become a full fledged e-sport
