Dusking does not spawn on his own, and requires the player to summon him with the Dusk Crown. He can be fought anywhere at night time.
Dusking floats in the air, moving towards the player while flinging a multitude of flaming purple projectiles, while summoning Antumbral Skulls. He also rapidly rushes at the player a few times every several seconds. When he reaches 8,000 health (9,000 in Expert Mode), he enters his second phase, where he gains a purple, enchanting aura, and starts to move erratically around the area, firing projectiles, and sometimes catching up to the player and floating above them, then moving away. This process repeats until he is defeated.
Dusking floats in the air, moving toward the player, flinging a series of projectiles at the player.
One of these projectiles are medium-sized, fast moving Shadow Balls that inaccurately home in on the player's position. These can be destroyed by touching them with a weapon, bullet, arrow, etc. They can phase through walls.
He sometimes spawns a very small, spontaneous explosion of 8 tiny Crystal Shadows in an octagonal shape. They are not very strong, or large, and do not home in on the player, but they can get in the way.
Dusking spawns Antumbral Skulls along with his projectiles. They move slowly, and follow the player.
Dusking moves erratically, and fires projectiles from himself at a massively increased rate. No longer spawns Antumbral Skulls.