Necromancer

The Necromancer is a Hardmode dungeon enemy. It will spawn in the dungeon only after Plantera has been killed.

It attacks by firing beams of purple light 6 times at the player. These beams are extremely dangerous, as the beams deal significant damage, reflect multiple times off walls and travel instantly, making it difficult to reasonably avoid its attacks. It also has a chance to inflict the Slow debuff.

Whenever it is attacked, it will teleport. With this and its attacks, it makes the Necromancer frustratingly hard to kill.

However, one easy way to kill them is to play their game with the Shadowbeam Staff that they drop. The easiest method by far is using the Piranha Gun or the Scourge of the Corruptor, both of which will follow them to wherever they teleport to so long as the trigger is held. You could also use the Magnet Sphere to shoot lasers hitting them everytime they teleport with great accuracy. It's also easy to kill them with weapons dealing lot of damage in one hit, like Grenade Launcher or Sniper Rifle.

They are immune to the Poisoned and Venom debuffs and only spawn in dungeons with a Brick Wall.