Nebula Pillar

The Nebula Pillar is one of the four Celestial Towers that appear during the Lunar Events. It can be found in one of four predetermined spots during the Lunar Events. It drops around 30-40 Nebula Fragments on average. It is the magic-themed Tower.

During the battle the pillar will start with a large force field around it, which can be taken down by slaying an unknown number of minions. Once the field is down, the pillar will become vulnerable, but minions will continue to spawn. The boss itself is fairly easy, having only 20000 HP and no direct attacks. While the boss may not be a threat, the minions it spawns deal high amounts of damage and can easily swarm the player if not taken care of. While near this boss, the player's screen will take on a dull purple shade, tinting all blocks, players, monsters, and the sky purple.

Summons:

Tips
A quick and effective way to kill all of the pillars is to use the North Pole directly and vertically above a pillar. Even if a player does not have any melee modifiers, if all of the snowflakes can make contact, the pillar should fall in less than 20 seconds. Another effective method to kill the pillar easily (If you have already defeated the Vortex Pillar) is to use the Phantasm with Chlorophyte Arrows.

Trivia

 * This pillar seems to resemble ebonstone, similarly to the Stardust Pillar.
 * The Nebula Pillar seems to have some sort of crystals growing out of it.
 * This is the only pillar to not have an attack that damages directly, as the Solar Pillar attacks with solar flares, the Vortex Pillar summons portals that either shoot lightning or spawn Alien Hornets, and the Stardust Pillar attacks by summoning white portals that either spawn Star Cells or Milkyway Weavers.