User blog comment:B214/Light Novel Volume 16 spoilers/@comment-1392308-20131019074749/@comment-1392308-20131019082101

I hope he won't be defeated either. His last defeat took place in Volume 11 (if you can even call t that, he only went down because he wanted to protect Asia and Xenovia, but apparently the author and Issei consider it a loss).

I can kind of understand Elucid dominating him but I apparently the fight doesn't finish. And I think Issei and Vali defeat Crom Cruach. So I don't think he'll get defeated by anyone. Just outmatched.

Tannin is a Dragon King that he has trained with so they would probably work well as Master/studetnt once again. Plus I like them together.