The vortex lingers for a significant amount of time after this attack. Flies in quick loops, spitting 5 Tooth Balls and forming a massive circular Sulphurous Vortex which draws the player into and around it.It gains a yellow glow in its eyes and some parts of his body, its charges and movement speed are faster, and its attack cycle is now modified: Transitions at 50% / 70% / 80% health, briefly gaining 25% DR and firing 6 Sulphurous Sharkrons upward as it does so. The Sulphurous Sharkrons explode into 2 damaging Sulphurous Gore chunks when killed or upon tile contact.Pulses, and fires 2 groups of 5 vulnerable Sulphurous Sharkrons, one group from the left and the other from right.Charges three more times, again accounting for the player's velocity.Killing the Tooth Ball, contacting it, or letting it live for 15 seconds will cause the Tooth Ball to erupt into 6 gravity-affected Trilobite Spikes in an even ring, along with a sulphur cloud at the center of the explosion.Spits five invulnerable Tooth Balls which target the player for 8 seconds, before turning themselves vulnerable and stationary after 10 seconds.Charges three times with short breaks in between, with the charge direction accounting for player's velocity at the time the charge began.The Old Duke's attacks function on a set cycle, being performed in this repeating order:

If the player exits the Sulphurous Sea or Ocean (edge 338 tiles / 676 feet of the world), the Old Duke becomes enraged and charges at a much greater speed and distance. While exhausted, the Old Duke's defense and DR are reduced to zero, leaving it vulnerable to attack. However, every 10 attacks, it runs out of stamina and becomes exhausted, pausing for 5 seconds before resuming its attacks. The Old Duke is normally very resilient, with high defense and DR.

When the Old Duke charges at the player, the direction it charges in takes the player's velocity at the time the charge began into account, aiming toward the player's predicted destination and potentially catching them off-guard. The Old Duke behaves similarly to Duke Fishron at its core, though most of its attacks are entirely unique and it features distinct differences in behavior.

It can also be summoned by fishing in the Sulphurous Sea with a Bloodworm post Moon Lord. The Old Duke can be spawned by finishing the Acid Rain event after Polterghast is defeated, appearing from a giant sulphurous tornado.

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