The Kosst Amojan had the power to revive the dead. It also granted great power to those it possessed that appeared to be telekinetic in nature. (DS9: "The Reckoning"; Star Trek: The Farthest Star: "The Final Prophecy")
The Kosst Amojan was believed to be able to harvest the pagh of its victims. It would grasp the ear of the recently deceased and strip their pagh from them. The reason for this was unknown, some thought it was just destroying the pagh, possibly to prevent the Bajoran from joining with the Prophets, others believed that it fed on the paghs of its victims. (Star Trek: The Farthest Star: "The Final Prophecy")
In 2372, the Kosst Amojan possessed Jake Sisko for its battle with the Prophet on Deep Space 9. It was eventually driven from Jake's body when DS9 was flood with chroniton radiation. (DS9: "The Reckoning")
In an alternate universe where the Dominion won the Dominion War the Kosst Amojan was freed in 2394 and possessed Skrain Dukat as its vessel for the Reckoning. In doing so it revived a deceased Dukat and gave him the strength to kill Kira Nerys.
The Kosst Amojan patiently waited within Dukat as he went on a murder spree, only taking control to harvest the pagh of Bajorans. When the Prophets' instrument arrived it asserted its control over Dukat completely.
The Kosst Amojan lost its battle with the Prophet. It instrument was transported to the Fire Caves by the Prophets and deposited into its flames prior to the Prophets' sealed the fate of the Pah-wraiths. (Star Trek: The Farthest Star: "The Final Prophecy")