It was very easy to forget that Donnie was a turtle with some human attributes, and not the other way around. One of the attributes he did not adopt was that mammalian circulatory system, which was barely keeping Tony warm in these conditions. It was fine, just another problem to solve, just as soon as Tony bought them some time by blindly grabbing from the first aid kit still on the ground and chucking whatever he found back the way they had come, to send a flurry of bats chasing after the sound. Meanwhile, he felt his way back up Donnie's arm to coax his head closer, tucking it into the warm crook of his neck, trying to at least keep Donnie's brain warm with a restless patting while his eyes darted in the dark like he could spot the obvious solution. The only thing that caught his focus was the doorway, now cleared of bats, revealing a larger, lower creature slinking in between them and the moonlight, facing them with such a clear intent that Tony's pulse must have been a trill by Donnie's ear.