Board Thread:General Discussion/@comment-4519633-20141022032431/@comment-5106672-20161206041407

The thing is, the OUAT villains are powerful. Very, very powerful, especially if they're in for more than just one episode. Short of kicking the bucket, though, that power can't be mantained, especially if they're making it to Team Heroes: there would be no story to tell otherwise.

Say, for instance, we need to face off the Snow Queen, and Rumple is fully reformed, using the Darkness for good like Merlin said. Snap!, the Snow Queen becomes a popsicle and the Frozen arc is over before it could even begin. Thus we need a shady Rumple lurking around, half in league with the Snow Queen to further his own agenda, so she can be a challenge for Team Heroes. Rumple can be the Dark One with other villains around because he's never truly reformed and, for whatever reasons, he doesn't interfere with their machinations. If he is reformed, then he needs to be puppet-mastered via the Dagger, like during the Oz arc.

So, once Regina joined Team Heroes for good, she needed to be rendered less powerful, otherwise BOOM, there goes the Wicked Witch, the Snow Queen, the Queens of Darkness, you name it. Now, Zelena is opening up to Team Heroes: she gets depowered because otherwise the Evil Queen can't stick around for more episodes.

The above also applies to Reul Ghorm, “bigger than anything”: if Blue could just fairy-blast anything away, any given crisis would be over in an episode and the Charmings would have no drama, so the Fairies are basically harmless in Storybrooke even though they have their wands and Fairy Dust back.

So, the rule is: the more of a hero you get, the less your magic can be effective in order for the plot to be serialised.