If Then is a game of co-operative pattern solving.
One player is the knower, who reads the custom rule for the round, and tells the other players whether their guesses are right or wrong. Everyone else is a guesser; they take turns choosing a card from a display and placing it in the line as a guess. The guessers win if they successfully shed all of the cards from their hand before running out of cards in the draw pile.
Custom rules may be based on the size, value, and/or color of the number and background. Higher level cards offer more complex challenges.