I know there is two of each element. It depends on whether you get the one where you get an effect on a lvl up or when you die. I can't really tell you what level they are but I know they are high like in the 40's and 30's and they have a 100% chance of happening.

I used to think there was a pattern in the color, cold blue fire red etc..but I've seen a green cold so...

and the blood ravens is pretty much a no trader...pretty common...