Attached character cannot be declared as an attacker/defender against the Pact's controller, and cannot enter challenges using card effects (e.g. Wardens of the North, Winterfell Kennel Master, Summer).
Note that the Forced Interrupt triggers before attached character actually leaves play. So if multiple characters leave play simultaneously (Valar Morghulis, Wildfire Assault, Marched to the Wall), you can sacrifice a character that would be killed or discarded anyway.
- If Crown Regent redirects a challenge in which attached character is participating to the Marriage Pact's controller, attached character gets immediately removed from the challenge.