I liked the arcade feel of this a lot. Controlling both with wasd, but having the option to solely control the blue ship was clever, and I felt that it added control and some nuance. Merging the ships together and being progressively bigger is a good use of the theme. Unfortunately it could sometimes feel impossible to avoid attacks or upgrades if you didn't leave combined mode, and you would lose all of the upgrades if you did. It's a cool concept that could be explored further, and with some more polish or time would be really fun. Good job!