I like the idea of a switching mechanic and general. The general implementation (as you said) also needs work. A few questions to get you started on improving the game:
- What textures do you want to add for the background and platforms? The game would look much better with them.
- Do you want to mark enemies you can switch with and those which are always hostile differently?
- How can you make combat more engaging?
- How can the movement of the player be fine-tuned?
Well done for making your previous work better. Iteration is key to making games. (or anything really!)