Does Bullet Time deal damage to all enemy units at one chosen battlefield, or to all enemy units that are at any battlefield?

Ruling: Bullet Time targets one battlefield. You must choose which battlefield when playing it, and it deals damage only to enemy units at that chosen battlefield.

Nuances:

• The card text uses "a battlefield" (singular) which indicates one battlefield must be chosen
• The card would benefit from clearer templating like "target battlefield" or "choose a battlefield" to reduce ambiguity
• You don't pay the power cost until the card resolves, only paying the 1 energy initially, which allows for strategic bluffing