Nightmare: Is there a list of cards the (arena) AI will nightmare into your hands? Or is it based mostly on other factors? A full breakdown would be best. Thanks!
DISCLAIMER: Most of my information on the AI is from before version 1.3 of the game.
List of creatures the AI will not nightmare:
Anything untargetable (graboids, immortals and phase dragons, although it may be possible with a mutant)
Malignant Cell (unless lobotomized, whether by means of the actual lobotomise skill or a replacement such as mitosis)
That is all.
For the factors in the decision, the ai chooses the creature that costs the most relative to your quanta totals. As such, it will always nightmare Light Dragons over photons, even if you have 75 light quanta and can play the dragons easily. The ai is also more likely to cast nightmare at all when your hand is less full, since that gives more health drain.
EDIT: Also, the AI loves nightmaring its own GotP, even if you have time quanta.