FMA Homunculi invade Middle Earth
The Homunculi of Fullmetal Alchemist Brotherhood invade the World of Middle Earth, halfway between the start of the Hobbit and Bilbo Baggins' 111th birthday party. The tunnels under Amestris' Central City are transported under the ruins of Angmar. The Homunculi are located inside of Father's chamber under the city. Father can not leave the chamber until the countrywide transmutation circle is completed, just as in FMA Brotherhood. How do Father and the Homunculi do? Can they take control of and then destroy Middle Earth?
Without Hoenheim around to screw up the circle and assuming alchemy works in Middle Earth as well as it does in FMA, they should pretty much have little to zero problems getting the big circle done.