Back on page 4 I jokingly suggested that maybe it’s Rumple’s shadow. Now, I’m seriously wondering about that.
1) He really got sucked into that vortex too and really had to dig in with his dagger to stop from going. Maybe a part of him did go.
2) Perhaps from having used the dagger, while digging into the hole, it released some type of magic.
3) If it were a part of Rumple, why wouldn’t he be collecting lost boys? He’s be searching for his lost boy and that’s why when Bae said his name the shadow started coming around.
Maybe Rumple in a round about way is responsible for creating Neverland and lost boys. They did say that something comparable to Red being the Wolf and Rumple being the crocodile was coming.