House Lannister. Non-Loyal.
Character. Cost: 3. STR: 3.

Kingsguard. Knight.

Interrupt: When a card is discarded from an opponent's hand, remove it from the game instead of placing it in his or her discard pile.

Ser Meryn Trant simply did not care.
Alexandre Dainche
Dragons of the East #29.

Link: Decklists

Ser Meryn Trant

How does this work with something like Missandei? or Ser Jorah Mormont (LMHR)?

Would it depend on first player to have it decide which way it resolves?

First player has the first chance for interrupt. — Korppi 9

Rules FAQ

  • If multiple replacement effects are initiated against the same triggering condition, the most recent replacement effect is the one that is used for the resolution of the triggering condition. Ex: Your opponent triggers Missandei to put her into play instead, then you trigger Ser Meryn Trant to remove her from the game instead.

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. — Duckbringer 63
However, some events have cost of discarding cards, and then those cards you could trigger Meryn on. — Duckbringer 63