"Mongols are tough!" - well, of course they are! And there's a very good reason for that, I'm afraid... let's put the puzzle together finally, considering some hard facts...
Mongols tend to appear suddenly from nowhere (out of a clear blue sky, so to speak). With huge armies. Using military units unknown in the civilized West. They are enormously determined. Boldly going everywhere. They are physically tough. Suffer no attrition. They possess extraordinary mental capabilities. Their rulers are multitasking virtuosos, being able to manage directly even couple of hundred provinces with a full efficiency and with no apparent signs of stress. In certain cases, they might become fertile in a very young age and show hermaphroditic tendencies. History has witnessed Mongol bachelors having 6 sons by age of 5.
And one of their coat-of-arms is somehow familiar...
Iturgen of Esfahan, afflicted wunderkind, retired ruler of Il-Khanat