About the Red Viper's ability, he doesn't kneel to attack. So my question is , can i kneel him to attack in some occasions???

No. Constant/passive abilities like that are not optional. If you have fewer characters, the Viper doesn't kneel when you declare him. You cannot choose to ignore it just because it would be more convenient to kneel him.

Thanks, that was very helpful. Now i know where the weakness of the RV lies.

We now have another confusing question. My friend played Beric Dondarrion (can't be killed or discarded if now pwr on your house card). Then his opponent take control of Beric (he has pwr on his power card). My question is , in this occasion, can he kill Beric now while he is contolling him.

Thx a lot

Yes.

xqg5009 said:

The words "you" and "your" on cards are always read from the point of view of the controller, not the owner, of the card.