I suppose I cannot decide to kneel him when Wall is standing?

Obvious reason - Castle Black.

If The Wall is out, you cannot choose to kneel him when you declare defenders just because it would be convenient. That part of his ability is continuous, so you don't get a choice on when it does or doesn't apply.

However, his standing when declared doesn't stop you from using Castle Black on him. Castle Black does not require the target character to be kneeling, nor does the standing need to be successful before the +2 can happen (the two effects are completely independent of each other because the word "then" doesn't appear between them). You can use Castle Black to boost his STR by 2 when he is defending, even if he is already standing.

It is hard for me to belive that Castle's Black : "choose and stand" can be interpreted that way. 

Anyway you seem to be sure about what you are writing so, since this empoweres my favorite faction i have no reason to continiue

Thanks.

"Card effects might be preceded by costs, triggering conditions, play restrictions, and/or play permissions; such elements are not considered effects."

- So since "choose" is part of the triggering condition for selecting targets, it is not considered part of the effect.

"Once initiated, players must resolve as much of each aspect of the effect as they are able, unless the effect uses the word 'may.'" 

- So once you trigger Castle Black, you resolve the +2 even if you can't resolve the stand, and vice versa.

"A card ability can only be initiated if its effect has the potential to change the game state. This potential is assessed without taking into account the consequences of the cost payment or any other ability interactions."

- So, while it would not be legal to trigger an effect that just said, "choose and stand" on a character that is already standing (because the game state cannot change by standing a character that is already standing), it is legal to trigger a "choose and stand and give +2 STR" effect on a character that id already standing (because the game state changes when the character that is already standing gets +2).

The interpretation works out just fine.

szczudel meet ktom.  he is our lord and master of rules interpretations.

Waking the Dragon has the same initial text.

Costs use a "do X TO do Y" format as described in the rules pdf.
As neither Castle Black or the near identical Waking the Dragon use TO, standing is a result of the action, not a cost.

For example:
After you win a power challenge, sacrifice Dothraki Sea TO do something.
Action: Kneel a Dragon character or Daenerys TO choose something and burn it.
Challenges Action: Kneel Margaery Tyrell TO choose a character. That character's beefed up.

Marshalling Action: Kneel Reducer TO reduce the cost of the next character played.

Waking the Dragon actual text
Action: Choose and stand a unique targ character you control. At the end of the phase, if that character is still in play, return it to your hand.

It would say "Stand a unique targ character you control TO return it to your hand if it is still in play at the end of the phase" if standing was a cost, but it doesn't use the cost construct. Instead, standing is the effect of playing Waking the Dragon in addition to pulling card to hand later.
 

Thanks guys for all the explanations. No I get it without any doubts.

Would it be possible to use his interrupt to put The Wall into play, and then trigger The Wall's interrupt in the same interrupt window?

The Wall:

Interrupt: When the challenges phase ends, kneel The Wall to gain 2 power for your faction.

Interrupt window is still open afer triggering(and resolving) Mormont's ability so yes, it is!

Can I play a Night's Watch character for free if noone challenged me at all the entire round? My friends are saying you have to be challenged and then successfully defend in order to use his Interrupt.

Can I play a Night's Watch character for free if noone challenged me at all the entire round? My friends are saying you have to be challenged and then successfully defend in order to use his Interrupt.

You can still trigger it. You did not lose a challenge as the defending player during the challenges phase, thus fulfilling his requirement. We'll wait for an 'expert' to arrive to clear this up lol.

You can still trigger it. You did not lose a challenge as the defending player during the challenges phase, thus fulfilling his requirement. We'll wait for an 'expert' to arrive to clear this up lol.

Krupp is entirely correct (don't doubt yourself!) - don't read more into the card than what is written on the card "If you have not lost". It doesn't say "If you have won every challenge initiated against you".

Your friends are liars. If you never had to defend a challenge, then you obviously never lost one.

"Put a [Night's Watch] card into play from your hand."

Does this include an event? I'm wondering if Take the Black event card is eligible for this if it's playable during the dominance phase only.

You [marshal] or [put into play] characters, locations, and attachments.

You [play] events.

can i put himself at play?

If you already control Old Bear in play, he can put another copy of himself into play as a duplicate (let's say you found him from an Arry draw).

If the only copy of Old Bear you have is in your hand, no, he can't put himself in play. From the RRG: "Card abilities on characters, locations, and attachments can only be initiated or affect the game from an in play area unless they specifically refer to being used from an out of play area, or require that the card be out of play for the ability to resolve." 

If you already control Old Bear in play, he can put another copy of himself into play as a duplicate (let's say you found him from an Arry draw).
 
If the only copy of Old Bear you have is in your hand, no, he can't put himself in play. From the RRG: "Card abilities on characters, locations, and attachments can only be initiated or affect the game from an in play area unless they specifically refer to being used from an out of play area, or require that the card be out of play for the ability to resolve." 

I don't see why not. When you check the play restriction (a NW card in your hand) another copy of the Old Bear is a valid target, so sure. Dupe away!

Read that post again

Read that post again