Thread:Zf6hellion/@comment-24913533-20140605060958/@comment-1493741-20140624140204

Any he wants to. He can introduce characters, events, alter the scenario, whatever. The only thing that matters is what A and B have decided on. A general rule of ettiquette would be to not directly affect someone else's character though. As in, lets say Person A attacked Person B.

Person A should describe the attack, but not its impact, if the attack hit at all should be left up to Person B.