This video showcases a strat that I found initially on accident, getting Yawn stuck. It's tough to set up, but it's safer if pulled off properly and allows you to not have to move at all to get slashes on him, which saves time and heal items. 2 ways to get him stuck are in this video, one being safer, but harder to do, and the other one, which is riskier, but easier as it's more likely he will get stuck.