Complex sentence: Mulan wants to make the trade, but Snow suggests they re-establish contact with Henry in order to overpower Cora; if Snow were exposed to Mulan's sleeping powder, it should weaken her mental defenses enough to cause her to visit the netherworld.
Split into simpler sentences: Mulan wants to make the trade, but Snow suggests they re-establish contact with Henry in order to overpower Cora. Snow deducts that if she is exposed to Mulan's sleeping powder, it should weaken her mental defenses enough to cause her to visit the netherworld.