If a unit is targeted by Elder Dragon at Battlefield, and I move my unit from Battlefield to Base with a reaction, does my unit live or die?

Your unit will live.

According to RiftJudge FAQ #9919 and the 2026-04-29 Rules FAQ Clarification, Elder Dragon's play effect has specific targeting restrictions based on location. It targets "up to one enemy unit at [a specific location]."

Why your unit lives:

1. Targeting: When Elder Dragon is played, its "When you play me" ability is placed on the chain and your opponent must lock in targets at specific locations (e.g., "the unit at Battlefield 1").
2. Reaction: By playing a reaction to move your unit to your base, you change the battlefield state before the Elder Dragon ability resolves.
3. Resolution: When the Elder Dragon ability resolves (LIFO order), it checks if the targeted units are still at the locations where they were targeted. Because your unit moved to your base, it no longer fulfills the targeting restriction of the ability.
4. Result: Your unit is no longer a valid target for that specific location-based instruction and is unaffected by the damage.

Note: This is based on the specific mechanics of location-based targeting as clarified in the Riftbound rules updates.