The Lesser Stygian is going to be the simplest and easiest enemy in the game. The opening sequence of the game sets you up against these enemies for your tutorial. Their moves consist of a quick walk and a slow swing that is broadcast by their glowing weapons. The weapons that they use tend to be simple melee weapons though most give them a significant amount of reach.
The best weapon against these enemies tends to be Rebellion though Osiris can be quite useful for large groups. The worst weapon you could use is Eryx because the weapon has very short range (shorter than their reach) and knocks them away when hit.
In most situations, these enemies are just fodder to distract you from more aggressive or dangerous enemies. Because of their low health, it is generally a good idea to get rid of them first. This will give you more room to move around while fighting more difficult enemies.
