First of all sorry if someone asked before and if it has been discussed already.

I want to ask what are exactly cards controlled by a player - or under his/her control - plain and simple.

Do cards in shadows, hand, deck are considered under control of a player?

Example: For the purpose of standing Weeping water, may I put into play an Honor guard, now under opponent's controller ?

Is the Honor guard considered having changed control from mine to his during the process of putting it into play?

well, well. Thanks for your always kind replies here guys!

Kordo

Kordovan said:

While your hand, deck, and shadows area are considered under your control, they are considered out-of-play areas, and, as such, no individual card in these areas would be considered to be controlled by a player until it enters play.

For the purposes of your example, let's make the assumption you are referring to Winterfell Honor Guard. By using its text and putting it in play under your opponent's control during challenges, it did not, in fact, change controllers, because it wasn't under anyone's control until you put it into play on your opponent's side of the board.

Now, when your opponent fulfills the other part of the Honor Guard's text by winning a challenge with the army participating, then, when you take control of it, it would then be considered to have changed control from your opponent to you.

To make a long story short (I know.. too late)… The answer to your first question:

Do cards in shadows, hand, deck are considered under control of a player? No. Individual cards in these areas are " out-of-play," and are not under anyone's control.

2. For the purpose of standing Weeping water, may I put into play an Honor guard, now under opponent's controller ?

Is the Honor guard considered having changed control from mine to his during the process of putting it into play?

No. It is entering play under your opponent's control, and, thus has not changed controllers