Can multi-target spells re-target if a hidden card at a battlefield becomes a new unit after the spell is activated? Can you activate a hidden card after your unit dies to reclaim that battlefield?

Ruling: No to both. Targets are chosen when a spell enters the chain and cannot be changed afterward.

Nuances:

• Hidden cards that are revealed after a spell has entered the chain cannot become new targets for that spell
• A hidden card cannot be activated after a unit dies from a resolving spell to reclaim the battlefield