She nocked the arrow, which was good - they'd need that, because he could sense what it was. Killian knew, he could smell it, could feel that familiar prickle of deja vu skittering over his skin, "Chimera," he said, right away, because he did not question that. In the Enchanted Forest, when he'd been a part of that bubble of existence containing those who were immune to the effects of the Dark Curse (put in place by Cora), it was a bloody awful existence. The whole realm was essentially deserted, and hunting for food was difficult at times - which was why sometimes you had to take out a chimera and make it last.
At least with multiple parts to it, the meat did last for awhile.
"It's got three heads," he told Rosa, in a calm voice, "Go for the middle, the lion's head, with your arrows," the Captain instructed, drawing his sword. "I'll go for the snake at the same time, to make attacking easier." Because he knew what would happen - the snake would bob and weave and stretch forward, with venom at the ready to spew, and he'd have to time to exactly right to lob its head off. "If the lion is out of commission, the goat is forced to take over - and all it will want to do is run away." Whereas if you killed the goat first, the lion took completely over and the entire thing became about ten times more aggressive.
That was all the strategy advice he got to impart, before they took two more steps - and the chimera, hungry as it was, showed itself - heralding its arrival, and its intentions, when the lion let out a roar, which about shook the very earth.