When Player A controls Arena's Greatest on their first turn and Player B misses the trigger on their first turn, who is responsible for the missed trigger and should a warning be issued?

Ruling: When a battlefield is controlled, its controller is responsible for adding its abilities to the chain. Player A (the controller of Arena's Greatest) should receive a warning for the missed trigger that occurred at the start of Player B's turn, as missing it was advantageous and they owned the card.

Sequence:

• Player A controls Arena's Greatest after conquering it on Turn 1
• At the start of Player B's first Beginning Phase, Arena's Greatest triggers
• Player A (as controller of the battlefield) is responsible for adding this trigger to the chain
• Player B notices the missed trigger a full turn later and calls a judge
• Player A receives a warning for advantageous missed trigger (per 702.2.e)
• Player B receives a warning for angle shooting

Nuances:

• The Tournament Rules state that triggers caused by battlefields are controlled by the player triggering them, but this appears to contradict the Comprehensive Rules which state the battlefield's controller is responsible
• The CR explicitly uses Arena's Greatest as an example and states the controller takes responsibility for adding abilities to the chain
• Tournament Rules take precedence over Comprehensive Rules when they conflict
• The warning would only upgrade to a game loss if Player A had 3 warnings in the same category (e.g., 3 missed trigger warnings), not 3 warnings across different categories
• The rule requiring the controller to be the owner of the card source (702.2.e) was confirmed to apply in this case