Sure! Here's an example of a simple game that meets your requirements:
This game implements the basic mechanics you described. The player starts with a blue block and can merge it to become green. The player can then fight the enemies (represented by blue blocks) by tapping on the "Fight" button. The player's health and enemy's health are displayed on the canvas.
Please note that this is only a basic implementation and can be extended further with more features and animations based on your requirements.