I don't think this has been mentioned yet, and it may be a target issue.
A couple times now, I've had the AI cast 2 Rain of Fire/Fire Storms on my creatures when just one would have taken them all out, wasting a card. It just happened again so I wanted to mention it.
EDIT: I play a mono fire deck and none of my creatures have more than 3 HPs. If I had to guess why, it's because the first fire storm's animation(flame pillars) had not removed my creatures yet so it casts another if it has one.
you know, the ai isn't watching the animation...
I know the AI isn't watching it, but it IS watching the creatures it was trying to kill. There is a slight delay using Rain of Fire/Firestorm before the creatures are removed, and it's the animation effect. It's not instant like a fire bolt or any other instant. When I see the card played, the animation starts and the AI immediately plays another RoF/FS.
Anyways, it was just a thought on why the AI does this.
EDIT: Just witnessed this again, he didn't cast a double RoF/FS (was out of cards), but the animation of the one RoF he did cast killed the middle creature first, there was a small delay, then the other 2 were removed. It could be nothing at all, or maybe something *shrug* Just trying to be helpful if I can.