'I… I misjudged him.'
Shandil regretted the fact that he attempted to see Eren through his lens. He believed that he could take on Eren for quite some time before calling it quits. He knew he couldn't win against him. He was not so weak as to not be able to escape him either.
This was considering Eren and Shandil fought seriously and Eren did not have any trump cards he hadn't used in the battle yet. But Shandil did not think that the butcher was okay with someone else doing his job for him. He had employed Kirin just at the right time to get rid of Shandil when he was at his most vulnerable.
Shandil was just a quasi-C-Rank entity while Kirin had the powers of a Monster Overlord, which made her as powerful as an Expert ranker. The foreign mana invasion initiated by her quickly took over his mana circuits and wreaked havoc inside him. Despite his best efforts, Shandil couldn't launch even a modest retaliation.