I'm very impressed by the RPG mechanics and story! Also, the slimes and their animations are adorable, adding to my wanting to save the slimes. The particle effects, animations, and music were well done. 

However, the controls were a bit confusing and all over the place. Mouse to click buttons for menu navigation, but keyboard for everything else? You easily could've had a "press enter/x to proceed" since that was a key the player was already using. Or if you did want to go the mouse route for buttons why not also use the mouse to move the camera?

Also, a few upgrade buttons didn't work (Life, Strength, Vitality, and one more on that column that I can't remember the name of) as well as the pause button. This made the final battle and most of the other battles nearly impossible because I'd get 3 shot by the final boss, and would nearly die after most encounters from the lack of health. This led to me just running through everything while collecting crystals to complete it. 

The text box that came over the screen was quite distracting, maybe move it to only the top/sides of the screen so the action isn't covered up by text. 

Adding walls to the environment would've helped with the cave/lab atmosphere.

These small issues are easily fixable so overall well done! :)