1. How is the movement? Does any mechanic feel too weak/strong compared to the rest?
The movement is great. I think that all of the mechanics are about the same in terms of strength.
2. Is the fog too aggressive or too slow? If future levels occasionally had very fast fog for a speed challenge, would that be fun or just brutal?
To be honest, I struggled even getting through the tutorials part so I really can't say anything. Based on my experience with the game so far and what I saw during the play test demos, I think that I might need a lot of practice before that could be playable for me. Skill issue on my end
3. Are any specific sections too difficult or unexplained?
I think after more practice, everything would be a lot easier. I think that everything was explained pretty well. Maybe something to add is a how to menu?
4. Do you think having enemies to fight would add some extra flavor, or would it distract from the speedy platforming too much?
I think something like the fog who chases is good enough. Maybe change the fog into something different later.
5. Any bugs or significant exploits?
I was stuck on a ledge for a bit where you can't move using A and D but I was able to move it using the gun. Other than that everything was alright.