I understand this thread was made 2 years ago, but you seem to really want help, so here it is:
Try using the Legacy Launcher instead.
I noticed an incompatibility with your mod and All-U-Want. When you attempt to edit a mob using All-U-Want, the game will crash.
For reference, All-U-Want is an advanced inventory editor that also allows the editing of entities.
Mate, you've blown this out of the park for sure!
But, how hard would it be to add a creative mode in the game? Even if it wasn't like the creative mode in present versions? That would make this mod absolutely epic!
Sorry, I clearly did not read your post fully. I missed the /creative command.