This game is polished and the concept is neat, but you should encourage the player to separate more often. As it is now, the safest option is to run away from thr green enemies while you get rid of all the yellow ones, and only then separate to take care of the green enemies. It isn't as fun as switching more often.
Gmtk made a very informative video about protecting the player from themselves. I recommend you watch it if you want to try and fix that in your future games