"It was the agreement!" The other changeling piped up to save her comrade from the unicorn's threats. Crimson turned back to face her captive. When they had captured the pony originally, they had not expected anything much more than dealing with a relatively powerful mage. So when they released her from sedation, they were expecting her to exhibit the same magical weariness all unicorns did upon waking, rendering them unable to properly coordinate between hoof and eye, let alone cast magic.