Double Cross is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Choose another player. Look at that player's hand and choose a card other than a basic land card from it. They discard that card. At the beginning of the first upkeep in your next game with that player, look at that player's hand and choose a card other than a basic land card from it. They discard that card.