Arbiter

Arbiters are hand-shaped monstrosities which essentially act as an enhanced version of Inquisitors. These enemies are only found in the Cavern.

To avoid getting hit, it is advised to bait them individually into shooting and parrying their central projectile to kill them. However, this strategy is not very efficient when wielding an off-color shield. Another safe option is to use the Homunculus rune to slowly kill them, as the range of this power is larger than the Arbiter's detection field. In situations where neither of these approaches are possible (e.g. no shield, cursed), one can try to bait them on one side of the screen and quickly kill them from behind while they are firing at their previous location.

Behavior
Arbiters, like Inquisitors, only have one attack. They can spot players through walls and will attack them from afar, sometimes even off-screen, though they can attack only horizontally. Their attack consists of a flurry of 5 magic bolts distributed to cover an angle of ~90° in the direction they face, with the central bolt directly aiming for the player.

Upon death, Arbiters drop a sort of grenade which explodes to produce a six pointed star-shaped pattern shooting at every direction. Before it explodes, this bomb can be parried with a shield, or deflected by the Shovel, Spartan Sandals and other boot weapons, as well as by Wave of Denial.

Unlike most mobs, Arbiters cannot teleport to the player on Nightmare and Hell difficulty modes. Note that only one Arbiter can attack you at a time if there are many of them within your ranged.

Elites
Elite Arbiters are ironically often easier to deal with than normal ones. Indeed, Elite arbiters can teleport to the player, and therefore can be baited to favorable fighting ground. A notable exception to this is when an Elite Arbiter spawns with the electric cage ability, which makes it particularly hard to kill without getting damaged.