When is a player allowed to see an opponent's decklist?

The correct answer is that a player is allowed to see an opponent's decklist only in the single-elimination playoffs of constructed-format tournaments. This rule is designed to promote fair play and sportsmanship during high-stakes rounds of competition. In single-elimination formats, the stakes are higher, and players may feel a greater need to understand their opponents' strategies and card choices to adapt their gameplay accordingly.

In contrast, during other phases of a tournament, particularly in the Swiss rounds leading up to the playoffs, players typically do not have access to their opponents' decklists. This restriction encourages strategic thinking and skillful play without the advantage of prior knowledge of an opponent's deck composition. After a match has concluded, players may choose to share or compare decklists for their own benefit or curiosity, but the formal rule allows this information exchange primarily in playoff rounds.