[Micah]

The combo of Mists and a damaging battlefield enchant is pretty much just a flat-out bug exploit, and I wouldn't be keen on playing with someone that was abusing it as such.

That being said the only real counters would be hitting him before he casts, preferably with something nasty like soul slay (or magic duel if he has low astral)...failing that flyers would only need to do one point of damage to send him packing with returning and waste his time, but it's just a stall strategy...air elementals can stormfly as well (might also help in taking out enough of the mist spawn to end the battle)