Hey! Nice submission. : ) This is a very cool concept and very unique too! I don't really recall playing anything with this mechanic. Sometimes it was a bit to slow though and a few times I was just sitting around watching it go from sad to happy to back again instead of mad so I would be able to kill the enemy. What broke it a bit for me when playing was the fact that your movement speed was not reset when switching levels. This made me loose immediately when completing a level because the next one had an enemy right beside the spawn point, and when I had to restart from level 1 I gave up sadly.
I think this is very much a buildable concept though! It's very creative!
Good work. :)