Okay I've completely forgotten then name of it, but the boss on the train in Timber. I think it was a fake Mayor.

You will see true power,
In the third of all, (I think it's the third boss in the game after Ifrit and Elvoret, if you don't count Diablos)
Two parts make it up, (The fight has two sections)
The first, a fearsome magic, (This is the second part so I'm sceptical)
The second, a fearsome man, (The man it impersonates, this is actually the first part of the fight though)
Together, they create me.

I'm fairly sure this is wrong even though it fits pretty well, but I'm too tired to think about it.