I like the concept quite a bit, good use of the theme, but I couldn't get past the first challenge after the first checkpoint. Seemed like there could be some more forgiveness there; not sure how to implement it, but it just feels like you instantly go into hardmode. (playing via browser btw). But it could be just that I'm bad at platformers.

The mechanics were fun and functioned well. The momentum made the platforming a bit hard and sometimes I died and never could see what killed me.

This was fun!  You did a really great job on your first jam!  This would be incredibly tough to speed-run.  When the player changes forms, are you changing to a new scene entirely and spawning the player in the previous position?  The response time on this was just a little slow and that made it harder to quickly transition, so I'm wondering if that part could be improved upon in the implementation.  

Congrats on your first game jam. Good little game the jumping was a bit clunky but overall nice little game.

I liked it. Most of the game was spent in cold-mode, and it felt like a fairly bog-standard platformer where you're a little slow. I think having more opportunities to swap between temperatures during a segment would showcase the main mechanic better - a good start would making the swap instant, so that you could swap mid-jump if you needed to. There's definitely good potential though.