The Shards

The Shards are post-Moon Lord bosses that spawn occasionally after defeating The Core, or by using the Arena Former. When summoned or spawned randomly at night, there will be a popup, saying "The Arena is forming..." and a minute later, another popup will appear, saying "The arena has formed!" and the player will teleport to an unbreakable arena in the sky.

Attack method
At first, two of the Shards will charge towards the player, then teleport to a random position. The other two stand back and attempt to blast projectiles at the player. The Void Shard floats in one spot, like a lunar pillar, and blast different types of projectiles at the player. In the Void Shard's second phase, when the other four Shards have been defeated, the Void Shard quickly teleports to random spots and fires projectiles, making it harder to hit it.

When all of the Shards have been defeated, the arena begins to collapse and fall to the ground. The player will be teleported to a random position in the overworld, and the arena will be shown falling in the background. The Arena can be found in a random spot in the overworld, completely destroyed and able to mine. when mined, the blocks all produce Sharded Ore, which is used to make an Arena Reformer that summons The Shards Recreated.