How can Nintendo claim ownership of the videos? I can see how they might claim ownership of the images and in-game sounds, but the commentary and actions made by the player is the ownership of the player. Taking control of content which they only have partial legal right to is still very much illegal and copyright infringement. They are basically knowingly committing commercial piracy, including sending knowingly fal…
I don't think that asserting ownership within YouTube is equivalent to asserting legal ownership of all of the IP involved. For example, I can't see them rebroadcasting any of these videos in another medium.