Gout of flame strikes enemy unit. Roll a D6 for each model in the unit: on a 6 it suffers 1 wound (saves apply normally). If the target is a flammable piece of terrain it will catch fire on 3+. Units can't enter burning terrain, and any models in burning terrain suffer 1 S3 hit at the start of their movement phase. Roll for every fire at the start of the Skaven turn: 1-2 fire goes out; 3-4 fire continues; 5-6 fire will spread to another piece of flammable terrain within 6".

Line of Sight

In this case a character with a unit must make his test just like evervone else. The rules governing flammable terrain specifically include woods, but players are left to determine for themselves what other features are considered flammable.