How can the dolphins take over?
The following scenarios may be upsetting to young children. Reader discretion is advised.
Scenario #1: Attack at the worst time.
World War III has ended. Nations all around the world have suffered heavy losses. Everyone everywhere is mourning their dead. At the worst time, the dolphins attack.
They start out by attacking swimmers (as usual), and then they work their way up to large ships. You must be thinking, "How can dolphins take down a large ship?" The answer is quite simple, they use their high pitched, particle-destructing sonar (Similar to the ultrasound used to breakup kidney stones) to attack the weak spots on the ship or they could gain assistance from whales. After the ships have sunk, the dolphins will use the wreckage to assemble vehicles that allow the dolphins to move about on land. These "dolphin vehicles" could be equipped with primitive weapons such as spears, catapults, or "rock guns." Losses could grow to thousands due to the fact that 50% of the population lives around the coasts.
Scenario #2: Telepathic Human Control
FACT: Dolphins have larger brains than humans.
Dolphins may have greater mental abilities than humans. They could very well have telepathic abilities. Instead of using telepathy to communicate with humans, they could be using it subliminally gain control of our minds. This causes us to "like" them and this could eventually cause us to obey their every command.
Scenario #3: Befriending Humans
Dolphins are very influential. Why else would SeaWorld, Green Peace, The Wild Dolphin Project, The Dolphin Institute, Blue Dolphin Alliance, and the Miami Dolphins be created? They all are designed to be aides for the dolphin's control. These cult-like businesses/organizations try to make you feel bad for the dolphins and they attempt to get you involved with their manipulative cause. Don't get corrupted by their "beliefs" or "facts"--they will try to deceive you at any cost.
Eventually, they will attempt to make everyone pro-dolphin. This will make people think it was the human at fault when the dolphins kill us and we deserve death. Therefore, people dying from dolphin attacks won't seem as bad--it was the human's fault.
Scenario #4: Aliens To This Planet
A long time ago, in a planetary system far, far away, lived a race of "super dolphins." In this perfect race of beings, there was some imperfections, or what I like to call, "retarded dolphins." The super dolphins wanted their race to be unblemished by the interbreeding with the retarded dolphins. So, instead of killing their simple-minded relatives, they sent them all to the nearest water-covered planet--Earth.
They may be retarded to the super dolphins, but they still pose a threat to us.
Scenario #5: Global Flooding
Dolphins have high pitched, particle-destructing sonar, as mentioned earlier. They could use this ability to loosen large chunks of ice from the poles and create ice burgs. (Titanic?) These ice burgs melt as they travel through warm water. This will add more water to the oceans and cause coastal flooding. Dolphins will then gain more and more control of the Earth's surface.