Aren't you already in a barrel?
Also:
When writing, do you people plan in advance, or do you improvise?
Generally if your scenes don't involve characters that are most definitely the mains of the other participants you have free reign to do whatever really. And even if they do you can improvise so long as you don't kill them off. With larger and more important narrative events... there's really not much of a structure to those either, if you take a look at our battle scene a few pages back you'll get what I'm talking about. We sort of just posted at random, playing off of the evolving structure of things as posts continued.
To further explain:
We have the framing situation and the main central elements. As we post we extrapolate and build upon those elements to build up the narrative. Occasionally we add additional elements and introduce events to further this. So long as the events aren't too out of left field, or fit despite being batshit insane we can work with them. This is the main bit to this, you can add anything to the story so long as you can make it work, or it isn't important enough to explain further, I mean, I introduced Andromeda after all... I need to do more with that character.