Marshgammon is a board game invented by Marshall when he was given control of the gang's game night in Game Night. It is complex and only Marshall understands it. Marshall explains that it combines all the best elements of all the best board games (except for backgammon, which is only used in the name). Marshgammon is, in reality used by Marshall and Lily as a means to interrogate Victoria, Ted's new girlfriend. By the end of the game night, Marshgammon had devolved into the gang sitting at the bar telling their most embarassing stories. In Ducky Tie, Ted mentions to Victoria that he's played Marshgammon a few times since that night and still doesn't understand the rules.
The rules of Marshgammon are very complex and only fully understood by Marshall himself although Barney understands some rules as well. However, there are a few rules that are explained by Marshall.
- Everytime someone says "WHAT?", a buzzer is sounded and that person has to drink.
- If you roll an even number when adjacent to the peppermint forest you "Marshall Out" and all of your chips go into the pot.