Sailors' Bane 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

This spell costs less to cast for each card you own in exile and in your graveyard that's an instant card, a sorcery card, or a card that has an Adventure. Ward (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays .)