Ser Meryn Trant

Does playing an event count as discarding a card from hand for the purposes of this effect? If so, when does the card count as being discarded - eg if meryn is put to the sword.

No, playeing an event is not discarding a card. —
However, some events have cost of discarding cards, and then those cards you could trigger Meryn on. —
Ser Barristan Selmy

Rules question.

If I choose to save a Lord with Ser Barristan, but Ser Barristan is cancelled, can I then use a duplicate to save said Lord instead?

Very late reply but the answer is YES. If cancelled Selmy will Stand and the character may be saved by another means. —
Melisandre's Favor

Does the character return to the original owner, following the forced interrupt? I would think so, but i'm not certain

Yes, it does return. Also see the review on "Ward" for a detailed look at taking (and losing) control of characters. —
The Iron Throne

Rules FAQ

  • The Iron Throne does not prevent an opponent from choosing and revealing a plot card, because plots are not marshaled, played, or put into play.
I assume the word “played” is referred to ambush, shadow, events. etc, not to reactions and actions from locations or characters, right? —
"Played" refers specifically to events. Shadows and ambush are "put into play". —

Rules FAQ

  • All "would be X" interrupts are eligible to be used before any "is X" interrupts. This means that an interrupt with the word "would" (such as "when a character would be killed") has timing priority over an interrupt without the word "would" to the same occurrence (such as "when a character is killed").

  • If an interrupt to a triggering condition that would occur changes the nature of that which is about to occur (such as saving a character that would be killed), no further interrupts to the original trigger may be used, as the resolution of that trigger is no longer imminent. For example, you have to trigger Ghost before Lysa Arryn, and once you save Lysa Arryn with Ghost, then you can no longer trigger Lysa.