Complex sentence: At the same time, Zelena creates a portal to get Merida and the other visitors out of Storybrooke just in case magic does get destroyed, unfortunately, the portal becomes too strong that it pulled Zelena, Snow, David, and Hook into it.
Split into simpler sentences: At the same time, Zelena creates a portal to get Merida and the other visitors out of Storybrooke just in case magic does get destroyed. Unfortunately, the portal becomes too strong that it pulled Zelena, Snow, David, and Hook into it.