Masters Edition III

Heavy Fog

Cast Heavy Fog only during the declare attackers step and only if you are the defending player.
Prevent all damage that would be dealt to you this turn by attacking creatures.

Cast this spell only during the declare attackers step and only if you've been attacked this step.
Prevent all damage that would be dealt to you this turn by attacking creatures.

Portal Three Kingdoms

Play Heavy Fog only after you're attacked, before you declare blockers.
This turn, all damage dealt to you by attacking creatures is reduced to 0.