I really liked the core mechanic here; the removal of regular movement is a fun implementation of a platformer, and the jump strength mechanic really adds to the usability. Very cool.
It seemed like the dice changing was just an aesthetic choice, but I think it could actually serve a mechanical purpose. Since the portal spawns near the "last" die, you could probably have them be numbered from 1 to 6, and require the player to do them in order? Then it adds an additional challenge (don't jump on 4 until you've jumped on 3) and avoid the situation I was in where I missed a die and had to go back to get it, and then go back again to the last die to find the portal.
Anyway, a nice little game; well done!