Apologies for an old topic, but I can't find our old discussion, maybe it was on the old message boards.
Scenario: My Jeyne Westerling attacks (STR 1). Opponent defends with Lady Genna (STR 2). I have Walder Frey in play (Deadly. After at least 1 defender is declared during a challenge,kneel Walder Frey to have him participate on the side that is currently winning the challenge.)
Walder Frey now participates in the challenge on my opponent's side, and my opponent wins the challenge.
Walder is deadly. According to the rulebook (p. 20), deadly is not based on "side," but on control. Since Walder is deadly and neither Jeyne nor Genna are deadly, my opponent must now kill for deadly.
Am I correct?