The card has:

Marshalling: Kneel Ser Ilyn Payne to choose and kill a character with STR 2 or lower.

Can I trigger that in any player's marshalling phase or just mine?

ed00011 said:

Note that there is one marshalling phase for every player. And yes, you may trigger it, no matter which player is currently active.

Rogue30 said:

Just to clarify: There is only 1 marshalling phase per round. Players take turns being the active player durring that marshalling phase. Players do indeed take take turns (going aroudn the table) for actions. However, only the active player is allowed to marshall cards into play as an action.