Attack on Titan (manga)/WMG

The Colossal Titan has the same powers as Eren
And his father has something to do with it, or he could even BE him.

The Colossal Titan, the Armoured Titan, Eren Jaeger, all share the same origin
This isn't necessarily surprising, since this has already been speculated in-story, but it would make sense if the formula that Eren's father used, was the same formula that created the three mentioned above, only from a different group of Humans.
 * Pretty much confirmed in the recent chapter, where we see the Female Titan's (cloaked) Human form, and her transformation back into her Titan form.

The Titans are scientific experiments on biological weapons of mass destruction.
This is similar to how zombies are often used in movies, and it would explain how the titans have so easily taken over as well as how