When Temujin shoots a flaming arrow to signal his troops to enter Urga, it is night, but when the troops see the arrow, it is daylight.
There are numerous historical inaccuracies regarding certain people, places, and tribes. The opening text explains that while based on true events, this story is fiction.
When Temujin throws a spear at a man in a stream, the wire guiding it is visible. The spear's trajectory is also wobbly.
In many of the "day for night" shots, the tents, animals and people all cast very strong shadows.
The bows that Temujin and Wang Khan use are modern recurves, which would make them approximately 700 years too early.
The landscape and vegetation are clearly those of SW USA and nothing like the Gobi desert.
The boom shadow appears on the chest of Genghis' brother.