You see An Observer Eye
Notes
Part of the Opticording Sphere Quest. It can also appear as 
when its cord is cut and after it's damaged for the first time.
Note that you can only obtain the Lightsphere once, if you kill it again you will not receive a second one.
Abilities
Great Energy Beam (0-5000+)Damage Taken From Elements
Physical 
Death 
Holy
Ice
Fire
Energy
Earth
Location
Replica Dungeon, past the Mysterious Device.
Behaviour
It is immobile, so it won't move. It will attack when provoked. An Observer Eye never retreats.
Strategy
Do not get close to it and walk around it using Magic Wall Runes to protect yourself from its sight. After using the machine north of the room, attack it from distance and do not use summons since they may trigger the boss' beams and target the players. Druids can use earth damage due to Boss's heavy death resistance.