There are 3 levels of Serpent Wards. The Serpent Wards increase in damage and hit points at higher levels. The Serpent Ward is magic immune
so don't try to dispel it.
You can aim Serpent Wards. Simply double click on one of the Serpent Wards to select all of them, then right-click on the unit you
want to attack. Hold down the alt key to see which enemy units are nearly dead.