Heh, I started the same thread not long ago
I'm guessing he gets out of the toybox, maybe through Momma Bosco's device? It was supposed to bring back the dead from the "other realm". Maybe it can actually bring people from different realms (like the realm of the toybox)? Ofc. that's all speculation but I kind of find it probable.
Momma Bosco: Look! I've finally completed my device! Time to get back to the living. *starts the device* *flash* Oh, and who might you be? ARGHHHHHHHHHHHH! *Opening credits start rolling*