The mares of Diomedes.
The four mares eat flesh and are crazy for killing. That was the story in the human world.
Sam doesn't if there is a change in the story or not, but there are a lot more details that were missed off and one of them is that the four horses do not just eat flesh and drink blood and they are most certainly not crazy.
It is just that they are possessive of their territory and they are extremely strong. Stronger to the point that it would seem unfair that an animal that was always only fit for a steed could possibly have the strength to compete with the apex predators.
The other thing is that the four horses are of different elements and have different abilities.
One of them has abilities of Water and Fire combined, the second one with the wind and lightning, the third one with the Darkness and Light, the last one with the metal and earth.
These are just basic elements, but their constitutions gave them further gifts.
