From all appearances the history of Earth-9966 closely mirrored that of Earth-616 until the faithful day when Reed Richards and his friends tested out his newly built spacecraft. In this reality, the four people aboard were killed in the crash, thus the Fantastic Four never existed in this reality. As a result the Sub-Mariner remained an amnesic derelict for a while longer. His memories were restored when his fellow tenants at a New York flop-house injected him with morphine and dumped his body in the ocean. The water revived Namor's memories. He then recovered the Horn of Proteus and used it to summon a massive sea creature called Gargantus to attack the surface. Even without a Fantastic Four in this reality, Namor was eventually driven back.
Finding his people in Atlantis, Namor married his long time lover Lady Dorma and then began plotting to take over the surface world. Allying himself with his cousins Namora and Namorita as well as Lemurian rulers Llyra and Karthon as well as the barbarian Attuma, Namor was able to accomplish this goal. Addressing the United Nations he told them surface dwellers that they could live their lives as long as they respected the will of New Atlantis. Namor then set up a new palace in New York City.
Eventually, the Fantastic Four arrived in this reality while on a quest searching for their missing leader Mister Fantastic. The Invisible Woman, the Thing and the Human Torch were all captured while Ant-Man ended up joining up with Betty Dean's resistance. While the Invisible Woman played on Byrrah's natural tendency for treachery, Ant-Man led the rebels on an attack on Namor's palace. During the fight Betty Dean revealed herself as a member of the resistance, prompting Namor and Dorma to call an end to the fighting. Byrrah took this opportunity to fatally shoot the Sub-Mariner, but he was executed by Namora shortly thereafter when she tossed him off the top of the palace. With Namor dead, Lady Dorma ordered her people to withdraw back to the ocean and let the surface dwellers live lives of their own. The Fantastic Four of Earth-616 the left on the Time Platform. 
Powers and Abilities
On par with Earth-616 counterpart