Builders' Challenge

A "Builders' Challenge" is a challenge in a few domino rallies where a builder would have to place dominos to make a line so that the rally may go on. This rather hard as they have to be fast but careful.

How it works
Here would be an example of a Builders' Challenge.
 * 1) First, we think of the challenge. Let's say that this triggers a catapult to hit a line removing a block to prevent the line to continue.
 * 2) The rally will just go on with a bunch of lines. The builders would have to do it (sometimes with an additonal obstacle) so that it will remove the block.
 * 3) The dominos should topple and remove the block.