Please read Commit comments.
- Managed to iron out the problems. Basically there used to be a conflict between the beginMove in Entity that I thought there was, since a prior edit you have made changed some part of it. However it's all good now. I modified the various beginMove methods you have overloaded so that it works for both of us. 
- Wrote a preliminary script, a draft of the stage1boss. It works right now, if you try it out, it should repeatedly attempt to bodyslam you. A word of warning - it attacks rather rapidly! You might lose if not prepared.
- As per your orders, I modified the MoveableEntity's continueMove function in order to allow velocity, rather than some constant you had declared before, to be factored into the calculation. Consequently everything all works out now.
Merger fixes
- Boss body slams the player