Bottle mod is something done by a certain storyteller/monster marshal that is done at random events. The things that go on vary greatly. Other than that the best answer I can give you is.....find out in game.
Fair enough! I just figured since it referenced OOG terminology ("mod") it was an out of game thing, but your answer is sufficient to give the jist of what I was looking for.
"You know the thing that makes gods fight against each other or marry one another? Or when something changes the minds of men to do wonderful or horrific things and no one really understands why? Whatever it is that makes those things happen... If there is a god that does that, I aspire to be that god."