Thank you for the advises. The 0 friction 2D physics material is already applyed. The problem of getting stuck, was bacause every single sprite have his own collider (to save time), and I have already change it and test that you dont get stuck (but as I put in a post bellow, I can't upload it because the jam is already active).
The visual representation of how high the character can jump is a nice idea, the only problem is that I'm not an expert in animation, however I'll try to do it when possible. For now, just know that you can jump from 5 to 1 block in each jump 1 less.
The checkpoint was something I was planing to make at the begining of the jam. The plan was to make the fountains checkpoints as well as a jump restart, but I also liked the idea of a hard gameplay. So to solve it, I was tinking of making a "Easy mode" or something, that makes the fountains act as checkpoints.
In my original design (in paper), the one way doors had an arrow, but I thought It wouldn't fit, so instead I make them, so that you (as the character) con pass from the opossite part of the wall (like in the block, the part that doesn't have wall), but maybe isn't as clear as I would like, and if the arrow option is better, I could try and change it.
Thank you again, it really helps me knowing what the community thinks about the game. <3