From what I uderstand,(no specific sources. sorry.) Moricho slows down an enemies organs to the point where they die. If Yaddle could defend herself against Sion for long enough Moricho to work against Sion, she would win. Moricho, I believe, will be Yaddle's only chance to defeat Sion. I don't know whether she will be able to defend long enough for Moricho to work.