The Hollow is proving to be one tricky enemy on The Originals. After the witch killed Elijah so that she could be reborn, Rebekah and Kol returned to New Orleans in "Phantomesque" to help their family. Unfortunately, that might have played directly into the Hollow's plans. Kol fell into a trap on The Originals when the Hollow resurrected Davina, which means the Mikaelsons might have lost an ally and gained a new enemy.
While Rebekah was out with Klaus destroying the thorns that can kill them, Kol went on a hunt of his own to find the Harvest Girls and beg for a chance to speak with Davina. They refused, leaving him passed out in the cemetery. When he came to, the Hollow appeared and offered him a deal: Davina for his loyalty. Turns out, the Hollow is a master manipulator, because she already resurrected Davina. She's being held behind a magical barrier in the cemetery, looking as alive as ever. She bleeds when the Hollow cuts herself, her blood a sign that she really is back — at least for now. As the evil witch quickly explains, she's linked her life to Davina's. If she dies, Davina dies with her.
The question now is will Kol actually let himself be manipulated by The Hollow? Will be be a double agent, spying on the Mikaelsons for the Hollow? Or will Davina keep him from betraying them to defeat the witch? If Davina really is back, then she knows the danger of the Hollow and is likely still focused on killing her. Something tells me she won't take too kindly to Kol doing the Hollow's bidding, even if it is to bring her back to life.