Amulet of Quoz 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

Remove this card from your deck before playing if you're not playing for ante. , Sacrifice this artifact: Target opponent may ante the top card of their library. If they don't, you flip a coin. If you win the flip, that player loses the game. If you lose the flip, you lose the game. Activate only during your upkeep.