Necromancers attack by rapidly firing beams of purple light at the player which reflect off walls multiple times. They travel at an extremely high velocity, being fired nearly instantly, and inflict the Slowdebuff. Necromancers teleport to a different location on-screen after firing six times or when being hit.
Necromancers can only teleport onto solid blocks. If there is no valid place to teleport to, they will remain in the same location.
They are only able to teleport while resting on a solid block.
A Necromancer's attack is always directly aimed at the player, regardless of obstacles.
In Expert Mode, Necromancers have a 0.13*1/800 (0.13%) chance to drop two Shadowbeam Staves at once. The chance to drop exactly one Shadowbeam Staff is 7.25*29/400 (7.25%), hence the chance to drop at least one is 7.38*59/800 (7.38%).
Weapons that stick to enemies are exceptionally useful, as they remain on the Necromancer after the teleport. The Piranha Gun, Daybreak, and Bone Javelins are viable options.
Weapons that deal high damage in single hits are effective against Necromancers. Weapons that fire multiple projectiles simultaneously may be able to land multiple hits before they teleport as well.
Weapons with homing capacities or minions can continue to track Necromancers after they teleport. The Sanguine Staff is particularly effective at this, often causing the Necromancer to rapidly teleport as it takes damage and quickly dies.