Issue with shields, I have observed.
Two cases:
AI plays Fog, than Gravity, wait a turn, plays fog.
AI has Fire Buckler out, than plays Fire Shield.
Also, One that may be more clever than fail...
Incarnate had two Retrovirii, and I had no creatures. He uses one of their effects.
Not sure if that's a fail, or if he did that just to power the death effects of his. Probably the latter.