There has been some dispute as to the synergy of Maester of the Sun and Darkstar. The argument seems valid that, because of the word "Instead" on Darkstar's ability, a card is never actually discarded for the Maester ability's cost. Has there been a clarification on this?

That is a legal move actually. You do pay the discard cost for master of the sun's ability, it's just that Darkstar has a replacement effect and instead of ending up in your discard pile, he comes into play. The fun part is that even if you cancel the master of the sun's ability with something like He calls it thinking or To be a kraken, Darkstar would still come into play because that's part of the cost of the triggered respons.

Ok, now I'm not sure if "is killed" is the same as "would be killed". If CS The Hound goes to discard he is definitely(?) considered killed. What about Stay of Execution? If I use it, is a king character considered killed?

Just going by the rules of English grammar, "If a King or Queen character would be killed, instead return it to its owner's hand." means that the character is put into its owner's hand instead of being killed, so it's not killed.

I had never really thought about the details of what's going on with Darkstar and Maester of the Sun before. Is Darkstar's wording supposed to be read as "If Darkstar would be discarded from your hand or deck, put him into play instead of putting him into your discard pile ?" Or is something funny going on with replacement effects and costs?

If a replacement effect replaces an action required as a part of a cost, is the cost still considered paid? To go back to Stay of Execution, if you somehow gave Old Bear Mormont or House Dayne Skirmisher the King trait and tried to use its ability with Stay of Execution revealed, would the ability resolve successfully? Or would the cost not be paid since the character was never actually killed? Or Stay of Execution's wording imprecise and should really be read as "If a King or Queen character would be killed, return it to its owner's hand instead of putting in its owner's Dead Pile?"

There is no functional difference between "is killed" and "would be killed."

When you are dealing with replacement effects, there are two different templates. How they are handled will depend on the wording used.

Wording #1 is what you see most of the time. It sounds like "if X happens, do Y instead ."

This wording deals entirely with the Moribund state (as in the case of The Hound or Stay of Execution) or, if the card starts from out-of-play (as in the case of The Darkstar), the way a particular effect resolves. In these sorts of replacement effects, the way that "X" resolves is replaced, but "X" is still considered to have resolved. So Darkstar is still discarded (it was a discard cost or effect that removed him from your hand even though he was put into play instead of being put into the discard pile), the King or Queen character is still killed (it was a kill effect that removed the character from play even though it is put into your hand rather than being put into the dead pile) and The Hound is still killed (even though he is put in your discard pile instead of your dead pile).

Perhaps one of the best examples of how this works with replacement effects is the Deathbound keyword. Take, for example, Forever Burning. It has the Deathbound keyword, meaning that you put the card in the dead pile instead of the discard pile whenever it is played. When you play the event and place it in your dead pile, you certainly didn't kill the event. In fact, you must have played it from your hand - as you must when you trigger an event - even though it is placed in the dead pile. You can still Respond to playing an event (for example, an opponent could still use Bronze Shield or Nomadic Trader when Forever Burning is played), but you can also Respond to placing the card in your dead pile (for example, with The Titan's Bastard).

The important part in all of these situations is that Y replaced how X mechanically resolves, but X is still considered to have happened, just under a temporary definition.

Wording #2 is much rarer. It sounds like "if X happens, do Y instead of doing X. "

The difference here is that the replacement effect specifies that Y completely replaces X. The original X effect is considered to be transformed into Y. This is the only time that X is not considered to have happened at all. The best example I know of this type of replacement effect is CS-Bronn. He specifically says that Bronn stands instead of killing the character. This means that the kill effect resolves as a standing effect and you can only Respond to the stand, not to the original kill.

So if Darkstar specifically said "If Darkstar would be discarded from your hand, put him into play instead of discarding him, " then he would only be considered to have been put into play and the combination of discarding him (into play) to pay for Maester of the Sun wouldn't work.

So don't assume that there should be more after the "instead" if it isn't printed there.

Thanks, ktom, that was very well explained (though I think I do need to assume there is more after the "instead" since I would read "if X would happen, do Y instead" as Y replacing all of X rather than just the destination of the card affected by X).

Then lets say it this way: never assume that what comes after the "instead" will make the replacement effect look like wording #2 above. Wording #1 is the "default;" wording #2 will always be specified.