Ruby Monsters is a "sister work" to Diamonsters, using the same art with some rules changes. Like the other game it uses a "butting" mechanic similar to Hol's der Geier. Players have a hand consisting of monster cards numbered 1-5. Each turn a card is drawn from the treasure deck, which can be a ruby card (with 1, 2, or 3 rubies) or a skull card. Everyone picks a monster from their hand and reveals it at the same time. If two players put out the same number those cards are removed, and then the highest card wins, except 1 beats 5. The winner removes the monster they used from their hand and the losers get their monsters back. There are three ways to win: get a total of five rubies, get two skulls, or get four treasure cards of any kind. —user summary