The summonable creatures are from level 1 to 5 from left to right, the more the player kills the more they get happy. upon reaching certain limits of happiness (or boredom) or the player dying, the game will end and the player will give a feedback according to the state of the ending.
You probably couldn't get the player to kill enough mobs in time. the balance is probably off. but hopefully the idea of the game was clear.