I teach a game design course at the local university and one of the things that struck me in my research for the class was the idea of an object in a game having multiple uses. For example, the dots in Pac-Man have many uses (This is taken from the superb book The Art of Game Design by Jesse Schell) :  

1. They act as a short-term goal: eat the dots close to me.

2. They act as a long-term goal: clear the screen of dots.

3. They slow the player down, making eating them a more dangerous than travelling down a clear path.

4. They add to the players score.
 
5. Collecting enough dots rewards the player with an extra life.  

In the earliest versions of this game I knew that the robot would not be able to jump and needed certain kinds of blocks to attach to after extending itself. It was a short leap to realize that a block would then fall down and cause damage to the player if you didn’t move out of the way in time. However, you could use a falling block to damage certain kinds of enemies achieving two things – a way to elevate yourself and a limited weapon

Similarly, the functionality of the slime grew from the same thinking. Initially, you just had to clean up the slime but there wasn’t any reward for doing so. I realized that being in the same room as the slime caused your damage to increase and so, by running over the slime and destroying it, your damage decreased. But collect too much slime and an egg forms from which a green spiky enemy emerges and flies around randomly. It used to be that touching a green enemy would cause the player damage but now they do not – I defanged this threat because players would bump into these creatures while moving around the screen, not seeing them in time, which is unfair. Still, two green enemies that touch each other turn into an angry enemy that hunts down the player (In the current demo build this happens infrequently but I’m going to make it a more common occurrence).

Development of the game continues, albeit very, very slowly. More thoughts later.