If my opponent plays Elder Dragon and targets my unit at Battlefields, and I play a Hidden Emperor's Divide to move them to Base, do they still die?

Your unit will live.

According to RiftJudge FAQ #9919, FAQ #10915, and the official Rules FAQ Clarification (2026-04-29) regarding Elder Dragon, its "When you play me" ability has specific targeting restrictions based on location.

The Sequence of Events:

1. Playing the Ability: When your opponent plays Elder Dragon, its "When you play me" ability is placed on the chain. Your opponent must lock in targets at specific locations (e.g., "the unit at Battlefield 1").
2. Reacting: You play Emperor's Divide from Hidden in response. Because it is played as a [REACTION], it is added to the chain on top of Elder Dragon's ability.
3. Resolution Order (LIFO): The chain resolves in Last-In, First-Out order. Emperor's Divide resolves first, moving your unit from the battlefield to your base.
4. Check on Resolution: When Elder Dragon's ability attempts to resolve, it checks the location of its target. Because your unit moved to your base, it no longer fulfills the targeting restriction of the ability (which required the unit to be at the battlefield).
5. Result: Your unit is no longer a valid target for that specific location-based instruction and is unaffected by the damage.

As stated in the official clarification: "If you play Flash [or any other reaction] in reaction to the play effect of Elder Dragon, any units that are moved to a location other than the one where they were targeted will no longer fulfill the targeting restriction of the Elder Dragon play effect and will be unaffected by the ability as it resolves."