Can Fox-Fire target a Shen that is played as a reaction to Fox-Fire being put on the chain?

Ruling: No, Fox-Fire cannot target Shen. Targets are chosen when Fox-Fire is put on the chain, before you can react with Shen.

Sequence:

• Fox-Fire is played and targets are locked in
• Opponent can then react with Shen
• Shen resolves first (as a reaction)
• Fox-Fire resolves with its already-chosen targets

Nuances:

• You may have to modify which target receives damage when Fox-Fire resolves, but you cannot expand the pool to include new targets that weren't available when Fox-Fire was initially played