Booby traps

During the Stygian Wars Alpha Legion controlled stygian forces made extensive use of booby traps when fighting on the defensive or when engaged in an insurgency campaign.  Most common types of booby traps were the simple trip wire connected to a grenade bundle as seen below.

Of particular note in the examples above are the use of fuel cans and two different grenade types.  A Fragmentation grenade with a shortened fuse would go off rupturing the fuel and sending it spraying outward only to be ignited by the phosphorous grenade turning the area into an inferno.  These types of booby traps had a hideous effect on morale for imperial forces that suffered casualties from them.
Another type of trap was the remote grenade launching trap as seen below.  Vehicle smoke launchers were tied to a motion sensor or remote and the smoke grenades replaced with fragmentation grenades.  Triggering this trap resulted in four grenades being launched into the midst of the unwary.  These traps although rare made breaching any building extremely hazardous.

Finally the general purpose IED was frequently employed against Imperial columns and spearheads.  The explosion remotely detonated would damage vehicles as well as kill or maim groups of infantry.