Runesword 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

, : Target attacking creature gets +2/+0 until end of turn. When that creature leaves the battlefield this turn, sacrifice this artifact. If the creature deals damage to a creature this turn, the creature dealt damage can't be regenerated this turn. If a creature dealt damage by the targeted creature would die this turn, exile that creature instead.