The Queen’s Assassin combines nicely with Cersei Lannister, whose ability can ensure the trigger condition of having more cards in hand is met. It goes without saying that most of the time an Ambush could be facilitated by Tyrion Lannister and his ability to gain gold from intrigue challenges.
The Reaction could be devastating if played at the correct moment, against a strong set of opposing characters. The Ambush ability could also be used to upset the challenge math of an attacking opponent. Finally, The Queen’s Assassin can be played in as a regular character for 2 gold- this may be useful whenever additional intrigue icons or chump blockers are desperately needed.