In Dungeon World, if a PC deals "stun" damage to an NPC by using a weapon with the 'Stun' tag, what are the mechanical effects?
I believe the rule book states that a character that has taken stun damage must 'defy danger in order to do anything at all,' or something like that. Since the GM doesn't roll for an NPC to do things, how does this work in Dungeon World mechanics?
P.S. - I'm not asking about the narrative. Once I understand the mechanical effects, I can craft the narrative to fit it.