Awesome Metroidvania with super nice artwork. The music is also superb and creates a very immersive atmosphere. The idea that collecting other slimes to make them join you and then get upgraded is a really good interpretation of the theme of the jam. The controls are very well-tuned, which gives me a squishy feeling that makes me think that I'm actually controlling some slimes. Well done!
But I do have to point out that there is one little issue that some visual indication and feedback is a little misleading, which confused me at the beginning of the game. For example, the visual feedback of the high jump is not that responsive. I do understand that you guys want to make the slime feel slow and sluggish. Maybe adding some sound effects to the high jump could do it.
Anyway, I enjoyed this great game a lot. Satisfying presentations and level designs, I definitely gonna give your game 15 stars. NICE WORK!