If you would have to draw LOS through this terrain to see a majority of the target unit when shooting, then that targeted unit gains the Obscured Condition against that attack.
Restrictive
A unit moving through this terrain moves at half speed (It costs 2” to move 1”)
Deadly
If a unit would move thought this terrain or remains idle in it, that unit must make a Deadly Terrain test. (Roll 6d6 and take 1 wound for each 1 or 2 rolled)