Can you play Stalking Wolf to a different battlefield than the one where you killed a unit to pay its additional cost?

Ruling: Yes. Stalking Wolf's text states you "may" play it to the battlefield of the unit killed to pay its additional cost. Since this is optional, you can instead play Stalking Wolf to any other legal location, such as your base or another battlefield where you control units.

Sequence:

• Pay the additional cost by killing a Bird, Cat, Dog, or Poro you control
• Choose to either play Stalking Wolf to that unit's battlefield, or to any other legal destination

Nuances:

• The Ambush keyword allows Stalking Wolf to be played as a reaction to a battlefield where you have units, independent of where the cost was paid.