In the rule “Mansion Phase”, change “If an Explorer is the only Explorer in a room, and the Black Cat is also in that room, and if the Explorer did not cease to be Possessed by Katastrophe in the previous step of the current atomic action, then that Explorer becomes Possessed by Katastrophe.” to

If an Explorer is the only Explorer in a room, and the Black Cat is also in that room, and if this Explorer did not cease to be Possessed by Katastrophe in the previous step of the current atomic action, then any Explorer currently Possessed by Katastrophe ceases to be Possessed by Katastrophe, and the Explorer in the same Room as the Black Cat becomes Possessed by Katastrophe.