Caïros is found arguing with Farlin on a beach, accessed by following the path west of South Span Checkpoint to a area with a ship that sailed from Moonrise Towers at X: -212 Y: 87.
Conflict between these two is inevitable, although the party can decide whether or not to get involved. If approached, the party is drawn into the conversation. Farlin explains that she is from the Guild, and asks the party for help. If the party opts to help Caïros, he insults them and both parties turn hostile. If trying to assist with a peaceful understanding, Caïros and Farlin turn hostile, and if waiting too long to intervene, the two begin fighting on their own.
If Minsc is brought along, he can try to explain that he is the Stone Lord, but Caïros does not believe him.
Normal weapon damage + Superiority DieWeapon damage
Focus your attack on your foe's hands and possibly force them to drop the weapons they are holding.
Slam your weapon into the ground, dealing additional Thunder damage equal to your proficiency bonus, thunderously impacting nearby foes and possibly pushing them away.
Range: Self
Recharge: 
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AoE: 3 m / 10 ft (Radius)
Melee: 1.5 m / 5 ft 
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Cairos on the Forgotten Realms Wiki