Cute concept! Although, it doesn't really match the theme, so I'm not sure if this game was intended for the Brackeys Jam.
The art is excellent, I really liked the pixel art animations as well. Goes to show you only need a few frames to really bring creatures to life.
I found the difficulty level high (which is a good thing generally) and I imagine if I had stuck with it for another ten minutes or so I probably could have gotten a handle on it.
The one thing that bugged me is that the controls felt a little loose. Tightening up the dragging and dropping could make a huge difference. Also the texture filtering on the green/red/yellow bars appeared to be linear even though the rest of the game has pixel art texture filters.
Overall great job! Please give my game a play and rating if you get time!