In ROTF we are introduced to the Nemesis. A large hidden ship commanded by the Fallen. In the first DOTM trailer we see and later confirmed to be the Ark on the Moon, a ship commanded by Sentinel Prime. Likely the expedition mentioned in ROTF by Sam. In the Super Bowl trailer we see the Decepticons have a fleet of ships invading Earth. These ships are smaller when compared to the Nemesis. I'm still hoping for the Nemesis to show up in DOTM serving as a mother ship or flagship of the Decepticon fleet. It starting to look like the Autobots and Humans best chance is the wrecked Ark and its likely stasis locked crew.