[Chel]

You had me intrigued by the first mention of the blindfold, but until then I wasn't hooked. Is there any way of moving the blindfolded brother into the very first sentence? That would make the start even stronger.

I'm glad I read on, and I would have happily read more. There were just a few things that jarred me a bit, but some of them may become more clear further on in your story. The following, though, needs to be changed.

That seemed unlikely to Serpes, whose head barely reached Corbis' waist. The eldest prince had jumped down from his horse, and one of the guards was cutting him from his clothing.

Sounds like the guard was cutting Corbis, not his clothes. Change to "One of the guards was cutting his clothing from him." While this part of the ritual is very dramatic and would make for a very nice scene in a movie, I personally thought it was a bit much to cut what I assume to be perfectly serviceable clothes to strips. Maybe Corbis could be wearing a special robe for the occasion? One that is buttoned at the shoulders maybe?
Oh, and if he had his hands free (which he had to as he was able to ride and dismount without help), he could undress himself, even while being blindfolded.

Another thing that struck me on my second read was that King Oreth's feelings were all over the place. He laughs and is relaxed with Serpes, but you also show he is a little bit worried about Corbis - but only a little. Oreth laughs so easily in this scene that it takes a lot of the danger out of the ritual - if you do want him to laugh, it could be a shrill, nervous laughter that doesn't fool even Serpes. If Oreth is normally a happy man who laughs easily, this would be a very good tool to make the reader understand the dangers of the ritual.

There's a few minor things I found, I've marked them in blue with suggestions for changes.

He couldn't possibly be killed. If any would survive this test, it would be him. Soon, Corbis stood naked bar his blindfold in the frigid air, and Serpes wondered how he could possibly (repetition, I suggest removing) not be shivering.

I think the ritual speech deserves a paragraph of its own.

“We are the wolves of man, born and raised by our pack but cast out into hardship. Through this trial you will prove your strength, or you will die. You stand as a beast. Clothed by hair and skin, armed with tooth and nail, you must prove yourself the equal of our world. Eat of raw flesh, drink of the stream. Hunt the greatest of prey. Flee from none (No one? Nothing? "None" breaks the rhytm somewhat.). Return to our pack in the skin of your foe, and a true wolf you shall become.”

Apart from that I don't have much to comment on, although I was a little confused about why Corbis would use such strength on his little brother. It wasn't nearly confusing enough for me not to want to read more, though, and as a first scene, this has me hooked and wanting to know more about King Oreth, Serpes, Corbis and their society. Very promising!