If I play Promising Future and my opponent plays Brynhill Thunderstrong off of it, do I still get to play my card off of it?

Ruling: Yes, you still get to play your card off of Promising Future even if your opponent plays Brynhill Thunderstrong off of it.

Sequence:

• Brynhill becomes the first pending item and will be played first when finalized
• Brynhill's "when I'm played" ability enters the pending chain
• Other players' cards from Promising Future will finalize
• Brynhill's "when I'm played" ability finalizes after their cards finalize

Nuances:

• Brynhill stops you from starting to put new things on the chain after her ability resolves, but the pending rules mean she can't stop the other things coming off of Promising Future that are already in the chain
• All effects of Promising Future resolve before addressing anything the spell may have triggered (per rule 151.3.a)