Namor is actually one of the heroes seen least throughout Civil War, but his role is pivotal. He basically turns the tide, if youll pardon the water pun. Actually dont, I wouldnt pardon a water pun that lazy. Anyway, Just when it looks like Iron Man and the pro-registration forces have Captain America beaten, its Namor and his army who appear to swing the battle in Caps favour, turning up at the last minute to overpower Iron Man and friends. Namor has more of a personal stake in the battle than others, as his cousin was one of the New Warriors killed in Nitros blast so its no surprise that if one won't appear in Civil War, neither will the other. Shame really, because the panel where the Atlantean army attack would make a killer shot. Since we already know all the characters involved and roughly where their allegiances lie, an unpredictable character like Namor really shakes up a story like Civil War. His sudden involvement allows one side to grab victory from the jaws of defeat (until Cap surrenders that is), and makes for a more exciting climax. In terms of the MCUs final fight, things are probably going to be a lot more straightforward than if they were to introduce an enraged mythical prince to proceedings. Shame really.