Cute game.
Other than "I Need more content!", it would be nice to be able to see any status changes (summoned samplings, defense up/down numbers), and see the boss health.
Also I would recommend adding a simple pause menu, and more the Return to Main Menu arrow onto that. Can prevent the player from mistakenly pressing the Return/Restart arrow during the boss fight (like me).
If you plan on developing this further please let me know! Would very much like to help on get a fun project off the ground.