10. Tyrant
Tyrant is actually a creation of Galactus, so its origins would have to be changed in the Marvel Cinematic Universe, but that shouldn't be a problem given that the Scarlet Witch is about to be introduced - and she's Magneto's daughter (Magneto being a charater, like Galactus, who is not a part of the MCU). Galactus wanted to create a powerful living machine in his own image, so he did so and bestowed it with the power cosmic. He named the machine Tyrant and it served him until its desire for conquest caused it to secretly rebel. Galactus aside, Tyrant is itself a being who hungers for domination. As a result, it clashed with Thanos and, as a being of a similar power level to the Mad Titan, adding him to the MCU to compete with him for universal domination would be very interesting indeed and would add a completely new threat for the heroes to have to think about. Tyrant's powers included the ability to absorb and channel massive amounts of cosmic energy for its personal use - it could convert the energy into superhuman strength and energy projection. Also, thanks to its bio-mechanical form, the entity was capable of using psionics to control and manipulate technological devices and beings. It was also highly durable and effectively immortal.