OK, here's one.
What if Anti was one of Marvin's magic tricks? Like, Marvin made a clone of Jack, but he messed up which caused most of Jack's "bad" feelings ( Insanity, some anger, that sort of stuff) to split from Jack.
It would explain why Jack doesn't get as angry ( or crazy if you could call it) as a contrast to before Anti showed up. Also, Jack sometimes will turn to the camera looking scared.
Am I wrong? Am I right? I dunno ;-;
Since it's just a theory..A YOUTUBER THEORY ( jk, matpat ur cool)