You've found the cures to four deadly diseases. But what happens when those diseases get stronger? Worse yet, what happens when someone spreads them intentionally?! Return to the world of Pandemic with On the Brink and prepare for the unexpected. The three challenges included with this expansion evolve the base game mechanics in exciting ways. One disease might become a Virulent Strain and become more difficult to treat as the game goes on. Or you could introduce an unpredictable fifth disease with the Mutation challenge and watch it pop up in unexpected places. Finally, teamwork is even more important if a fifth player dons the mask of the Bio-Terrorist and spreads panic while moving secretly across the board. Try each challenge individually or combine them all for a major test!