In the co-operative game Magic Mountain, you want to help four good witches get down and off the mountain before three bad witches can do so.
The game board starts with six good witches near the top of various channels in the plastic surface covering the board; four bad witches are placed at lower intersection pints for these channels.
On a turn, you draw a colored marble from the bag, then drop it down one of the channels. If it hits a witch, that witch will stop the marble's movement. You then remove that witch from the board and place it on the closest space matching the marble's color below — that is, going down the game board from — that witch's current location. The marble will then start to roll again, possibly hitting another witch and causing it to move down the board, and so on. When a good witch reaches the pool at the bottom of the board, it needs to be hit by one more marble to remove it from the board entirely. Remove four witches before three bad ones, and you win!