When Volibear attacks a battlefield, does his damage trigger resolve before Grand Stratagem can be played?

Ruling: Volibear's damage trigger resolves before Grand Stratagem can be played. Grand Stratagem has action speed, meaning it can only be played when there is no chain. By the time the chain is empty and you can play Grand Stratagem, Volibear's trigger will have already dealt its damage.

Sequence:

• Volibear attacks and his trigger goes on the chain
• Volibear's trigger resolves, dealing damage to units
• Chain becomes empty and you gain focus
• Grand Stratagem can now be played for any surviving units

Nuances:

• Grand Stratagem can only affect units that survive Volibear's initial damage