Thanks for the feedback, that's why I made this thread
I wanted the freezing mechanic since the beginning because I didn't want players to be able to kill enemies by stomping them. About checkpoints, there will be. The stars also add challenge and replay ability.
Furthermore, I want to thank you for the feedback on the first enemy you have to freeze, because I didn't see that part from a player perspective. For me, it was obvious I had to freeze the bat to jump to the next platform. But for a player playing it for their first time, they'll probably scratch their head for a bit before realizing what they have to do. The game is more focused on platforming rather than solving puzzles, so they must know what to do at all times, the challenging part will be knowing how to execute it perfectly.
By the way, Blitz (Matz) and Mija share the same speed, amount of jumps and health. There's no difference between the two.
I can't confirm boss battles, since they're pretty lame in Bloxels. I can say the game will have a humongous difficulty spike, with the final challenges requiring all the skill you've gained throughout the game.