There are more than enough cases to justify me pronouncing AI as Artificial Incompetance.
But mostly I've seen it in the arena where I was trying to make a really simple deck and testing against another to avoid the upcoming mistakes of the AI,
like fractal a low attack power creature while having only 3 empty hand slots, or using explosion to destroy one out of 4 pillars instead of a golden hourglass...
I had this idea (or more likely a programmer's nightmare :p), to add for the arena an algorithm for each arena deck submitter to be able to "train" her/his deck,
by statistically altering the cases each card is played, like what cards are down, on hand, quanta etc.
By playing with the would-be-submitted deck a few to plenty games, one could change the behaviour of the AI playing this particular deck.
It's just an idea to see more complex and efficient decks on the arena to work as they supposed to.
Though if there's a case elements AI turns into skynet or something, I'd gladly stay with the retarded one