If I play Flurry of Blades before Dazzling Aurora triggers, then reveal Elder Dragon from Aurora and the opponent plays Star-Crossed in response, do all enemy units die from the 1 damage?

Ruling: Yes, all enemy units with 1 damage from Flurry of Blades will die before the opponent can play Star-Crossed. Elder Dragon's passive ability becomes active immediately when it enters the battlefield, making the 1 damage lethal during the mandatory cleanup that occurs before the "When you play me" trigger is finalized.

Sequence:

• Flurry of Blades resolves, dealing 1 damage to all units (damage remains marked)
• Dazzling Aurora triggers and Elder Dragon is played to the battlefield
• Elder Dragon enters play and its passive ability becomes active immediately
• A cleanup is queued as an outstanding task
• The HOT FEPR system pauses the chain to handle the cleanup before the "When you play me" trigger can be finalized
• During cleanup, the 1 damage on enemy units is now lethal due to Elder Dragon's passive, destroying them
• After cleanup completes, the "When you play me" trigger is finalized and players receive priority
• At this point Star-Crossed could be played, but the enemy units are already destroyed

Nuances:

• Passive abilities become active immediately when a permanent enters the battlefield
• Outstanding tasks (like cleanup) must be handled before the FEPR process continues with pending triggers