The long hinted at Megalodon on Nansha Strike! The shark had been seen in numerous dog tags, referenced by many developers, etc.
To activate the easter egg, 10 players need to gather around the buoy as seen in the picture below. After waiting for a bit, Megalodon will rise out of the water and will subsequently fall and crush all players. Thats what you get for not heeding the "Beware of Shark" warning on the buoy!