[Game concept project] Times Square

Hey ho, this is not dead! Stuff just got in between and then I sorta forgot it.
But I have been working on it a little, trying to implement those physics. It didn't go very well, so the other day I just removed everything and started from scratch. I encountered something that may be easy to go around, but it really annoys me and has left me clueless. I just tried to make the monster stop (freeze) when it hit the characters head, and then proceed falling when the character stepped away. The result is the monster bouncing up and down a few pixels on the characters head. This is really strange, because absolutely nothing in either the step or collision event says that it should ever move upwards. The only things that can give it a negative vspeed is either loading a negative _vspeed (stored vspeed, used when freezing and unfreezing) or colliding with the ground. It certainly does not collide with the ground, so it must be the _vspeed? Well yes, silly me, it is. The _vspeed is set to -1 as default, and explains it all. When I set it to 0 or lower the monster goes through the character instead, though. Did I also mention the game goes in laggy slow mo now?
Well that's a new problem then! Wouldn't mind if someone helped me with the actual stop thing though. If you are lazy here is the code, or you can download below for tweaking and testing.