Krovikan Whispers 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

Enchant creature Cumulative upkeep or (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.) You control enchanted creature. When this Aura is put into a graveyard from the battlefield, you lose 2 life for each age counter on it.