Fog

Place a line of fog, 6'' long, 3'' high, and 1'' thick
anywhere on the table as long as some part of it
is within line of sight of the spellcaster and all of it
is within 24''. Figures can move through the fog
with no penalty, but line of sight may not be drawn through it.
At the start of each new turn, roll a die.
On a result of 1 - 4 the fog dissipates and
is removed from the table.