Sometimes it's fun to try and combine multiple game boards or sets at the same time. We can always use the normal ways of adding two games together, but there are some other alternatives too...
In high school, a friend of mine mentioned he used to play "boxcar chess" with his family. This is a version of chess using two sets and four players on two teams. Two games went on at the same time, except whenever you capture an opponent's piece, your teammate gets to add that piece to their board. Thus, you had to play the opposite color of your teammate.
I don't know the details of how you add "new" pieces, but I assume you can spend a turn to place one of them in your back row.
I tried to adapt this for Stratego, since my family had two sets. I made the rules a bit too strict, however, and it wasn't all that interesting. I'd like to give it another try some day with more flexible rules.
Then, just last week, I was chatting with Brian about old war games (I really am only familiar with Risk and Diplomacy) and he mentioned enjoying "Double Risk" using two boards. The boards interact by including adjacencies between each pair of countries with the same names. Thus, if I wanted to get past Central America on board A (which has a bunch of armies on it) and I have a big force on Venezuela on board A, I could instead attack Venezuela on board B, then Central America on board B, then, say, Western United States on board B and on to Western United States on board A. I don't actually think this is a good Risk strategy, but I'm still bitter at that game for the power of cards...
A Domino-Covering Problem
2 weeks ago