The Serpents or Sea Snakes will attack any nearby hostile units, but will not stray far from where they were summoned. The player has no control over the reptiles but shares their Line of Sight.
Plague of Serpents can be used as emergency defense or to boost an early raid. However, the summoned units are weak and only deal average damage. They will be killed quickly by a determined attack, so Plague of Serpents should be used to support combat units already in the area. The Serpents are virtually incapable of disrupting an economy as they deal little damage to worker units. The latter on the other hand deal bonus damage against Serpents, so they can easily kill them. Heroes and standard myth units should also be avoided. Plague of Serpents should only be invoked on water as a last resort to secure victory in a naval battle or to distract enemy ships from attacking friendly Fishing Ships.