We apologise for the late review:
GDD
Nice to see the proper credits given to the creator of the template. The GDD is very well detailed; I could clearly see the team's vision. I would like to see some images, but I understand that with the time constraint, it has low priority.
The point of the GDD was met; it was very useful at seeing the mechanics that are still to be developed.
Gameplay
It started very floaty; there's no precision at all on the commands. The slime is extremely bouncy and hard to control. I see that combat and enemies are not properly implemented yet, just a couple of static assets.
Then I decided to treat it like a tech demo and explore. Everything fell into place. The floaty and bounciness meshed together with the grappling; I spent a lot of time just slinging me around as fast as I could, seeing how high I could bounce and if I could save a botched play. I don't know how much time I spend hurling myself from wall to wall, and the pleasant surprise when I messed up and fell, only to bounce super high and save the progress.
It was loads of fun; I think you guys are onto something there.
Art
Lovely art, even though simple for this stage. It's a blank canvas that can be painted however you wish.
Sound design
Really sweet BGM; it blended well with the feel and style of the game. The SFX were minimalistic and did a superb job. Very well synched and responsive.
Last thoughts
I will level with you guys: as it is, the game has nothing to do with the theme. The planned features could make it fit more, but at this point, I would advise the team to keep developing those core features you already had because I had a blast bouncing madly around. It was so much fun that I don't see how enemies or other things that would fit the theme will enhance the potential gem you guys created. As a pure platformer/speedrun/puzzle, this game has loads of potential.
Congratulations on your first game jam.