Let me preface this, by saying that I am still pretty new to the game.
Me and my father were playing tonight, I was playing Core Lannister and he was playing Core Stark. He played Eddard Stark and attached Nymeria to him. Nymeria's effect states:
Stark character only.
Response: kneel Nymeria to save attached character from being killed. If attached character is Arya Stark, she also gets +1 STR and gains stealth.
I proceeded to conduct a military challenge on him with a strength of 8 and he defended it with Eddard Stark. He lost the challenge so he should kill one of his characters. He decided to choose Eddard Stark, but because he had Nymeria he said that he should be able to kneel Nymeria to prevent Ned from being killed.
Is this legal? If so it seems that any character with Nymeria is invincible and the person can direct any lost Military challenge to whatever character Nymeria is attached to.
My thought was, that when a character is knelt, their attachment kneels with them to prevent things like this from happening. I need some clarification.