Unit Card #55 Archmagus Valpurgis has a special action in his text which states:
"Obsidious Bolt" - 3 Actions: Choose an adjacent hex as a direction and draw a line to the end of the map along every hex in that direction. Roll 2 green (light ranged) dice against every unit standing in this line.
Must you roll for accuracy on each unit in line of the bolt? This is not a normal attack action. So the normal attack parameters do not necessarily apply. In fact the above text does not really state that you are rolling for damage (though what else would you be rolling for?)