Board Thread:General Discussion/@comment-28883990-20160629232119/@comment-24674051-20160630171634

Before First Curse broke, everyone is trapped, except for Regina and Henry (and Emma once she arrived).

After first curse broke, only Henry and Emma can cross safely (as seen in "Going Home"). Gold's concoction allows for a way of safely crossing, but still dangerous once on the other side. Nothing prevented crossing though, in this case, you just lost your real memories and kept your alternate ones. We also saw Michael and John enter SB from outside, so entry was not prohibited at this point either, until Belle erected the barrier.

After Curse 2, you had Flying Monkeys performing border patrol, so there is no evidence one way or another whether you could safely cross. Then you had Elsa/Ingrid's ice wall which provided a physical barrier preventing leaving. And finally, you had the border that prevented reentry, except by use of Ingrid's scroll.

Curse 3 made it so that anyone crossing was transformed to a tree, at least prior to the UW. I think we need to understand what KIllian's death, combined with the tethering of magic, did to the border. There are simply too many variables in play at this point.