Reverse continuity cards are a bit confusing. To put it simply, they reference the state of the game one or more turns ago and play something depending on that. Probably the most common variety is a card that nullifies the effect of the previous card played. The exact order of play may need to be recorded if anyone makes such a card to revert to the situation more than two turns ago. Large-scale time travel, though, is a good way to confuse everybody.