1) Flaps Extended - The simple reason Vmc decreases with flaps extended is because a greater component of horizontal lift to counteract yaw. There may be contributing factors, but they are secondary.
2) Gear - " Vmc does not necessarily decrease, and control does not necessarily improve with the landing gear in the extended position. The ‘stabilizing effect’ of landing gear on individual aircraft is not tested. Vmca is determined with the gear in the retracted position, and therefore the extended gear’s effect on Vmca is unknown and would vary between different airplanes and gear systems." - From a Multi Engine Instructor Document