On the way back to the bunker the Winchesters and Jack stop at a hotel and are met by Donatello the prophet. Amara ate his soul but he has been mentally making the moral choice ever since, he was drawn to Jack's power. Jack reads The Bible to learn more about himself and his family. Realizing he'll need more protection the Winchesters try to get him warding tattoos but he reflexively attacks the tattoo artist for hurting him and his body heals the ink away. Dean takes this as proof Jack will turn evil, while Sam thinks it's because he lacks control. Meanwhile, the final Prince of Hell, Asmodeus, takes charge of Hell until Lucifer returns, disguising himself as Donatello to trick Jack into freeing the Shedim — Hell's darkest creatures — to be a hero. The brothers and the real Donatello appear and when Asmodeus hurts them, a flicker of Jack's power makes him flee. At the bunker, Dean admits to Jack he will kill him if he turns bad. In the alternate world Lucifer protects Mary, intending to trade her for Jack when they get home. They meet an alternate version of Michael whom killed his world's Lucifer. Michael is the stronger of the two, keeping this Lucifer alive because he needs him for something.
Source: Wikipedia
Source: Wikipedia
Jack is good and cute and Dean should be much nicer to such a powerful being! But in saying that I am also so sick of annoying naive teenagers too, so maybe I can see Deans side a bit more. Being gruff will prepare Jack for the real world - if he ever gets there!