Kostya was right behind Terra as she sighted the den. He was suddenly feeling a lot less confident about tackling the cougar now that he was actually here but he shoved his apprehension away, confidence would aid him here better than second-guessing himself.
Peering out at the den he whispered to Terra, "Can you see if its in the den? I could try and distract it while you sneak in and take the deer." A simple plan, if slightly risky. If he shifted to his Optime form and used his bow he could probably keep the cougar at bay until it decided he wasn't worth chasing.
While he waited for terra's answer he lowered his head to his shoulder using his teeth to tug on a small knot which made his harness slide off his back when he pulled it, freeing him up to move easier no matter what the two ended up doing. This done he dropped himself low to the ground, kneading the ground beneath his paws as he glared out into the clearing.