Can you react to Grand Plaza's On-Hold trigger by adding units to reach the 7-unit win condition?

Ruling: No. Under the current rules, Grand Plaza's ability follows a "Condition, condition, effect" structure. You must have 7 or more units at the battlefield at the moment you hold for the triggered ability to be placed on the chain at all. If you have fewer than 7 units when you hold, the ability does not trigger and you receive no priority window to add units.

Sequence:

• During the Beginning Phase, you hold The Grand Plaza
• The game immediately checks if you have 7 or more units at that battlefield
• If you have 6 or fewer units, the condition is false and the ability does not trigger
• If you have 7 or more units, the ability triggers and goes on the chain, giving opponents a chance to react

Nuances:

• This ruling represents a change from previous rules interpretations where the condition was checked only on resolution
• FAQs #1423 and #1676, which allowed reacting to add units, have been deprecated