Shake Down

I do love 20s and letting a lucky roll really change the story. It provides a second element of narrative influence for the players, albeit a random one. You can’t plan on a natural 20: they just happen. It’s not quite the same level of story control as a firm plot manipulation mechanic (plot points or the like) but it’s neat. But it can lead to some pretty absurd situations that stretch credibility, requiring a little extra DM description panache.