The second half of the Rains of Castamere reads: "After you win an ITR challenge by 5 or more STR, kneel your faction card to reveal a Scheme plot. If that card leaves play, remove it from the game."

Sneak Attack reads: "You cannot initiate more than 1 challenge during the challenges phase."

I am curious if Sneak Attack is the scheme plot you reveal, since you already initiated an intrigue challenge, would Sneak Attack then prevent you from initiating further challenges?

Sneak Attack does not have the "When revealed," which is leading me to believe that the ITR challenge you initiated would have to be the last challenge for the turn, but it would raise the claim to 2.

Or, is there a certain ruling for this agenda?

The second half of the Rains of Castamere reads: "After you win an ITR challenge by 5 or more STR, kneel your faction card to reveal a Scheme plot. If that card leaves play, remove it from the game."

Sneak Attack reads: "You cannot initiate more than 1 challenge during the challenges phase."

I am curious if Sneak Attack is the scheme plot you reveal, since you already initiated an intrigue challenge, would Sneak Attack then prevent you from initiating further challenges?

Sneak Attack does not have the "When revealed," which is leading me to believe that the ITR challenge you initiated would have to be the last challenge for the turn, but it would raise the claim to 2.

Or, is there a certain ruling for this agenda?

You are correct, Sneak Attack prevents you from declaring additional challenges after the resolution of this Intrigue challenge but raises the claim to 2. Not a good use of Rains unless it's your third challenge.

Sneak Attack is a continuous effect that is active for as long as the plot is your revealed plot.

Because the effect it based on things that happened during the phase, It's "cannot initiate more than 1 challenge this phase" limitation looks back to the beginning of the phase; not just to the moment that it entered play.

So, if you use Rains of Castamere to switch into Sneak Attack, you will not be able to initiate another challenge (since you have already initiated one that phase). But if Rains of Castamere is your plot when you initiate the INT challenge, they use Rains of Castamere to switch to another Scheme plot, you would be able to initiate additional challenges (because Sneak Attack is no longer active).

But if Rains of Castamere is your plot when you initiate the INT challenge, they use Rains of Castamere to switch to another Scheme plot, you would be able to initiate additional challenges (because Sneak Attack is no longer active).

That cannot happen. With Rains of Castamere, you cannot reveal a Scheme (such as Sneak Attack) plot during the plot phase (these plots are not considered to be in your plot deck then), and you must kneel your faction card to reveal one during the challenges phase (and there's no way to stand it with a card effect).

Sure, because it's not like they could ever print another card that allows you to reveal a new plot card. But I suppose it's important for illustrative purposes of how continuous effects work to stick to the current card pool.

Sure, the situation you want to illustrate could happen with new cards (one that allows a player to stand their faction card, for instance).