Idea is good.
Just a few suggestions, if i may, in case you want to expand on it in the future.
The choice for the keys are placed too closed.
It would be nice to have multiple keys for the same action, so that it give players the choice of how they want to control it.
For a platformer game, I think responsive control is important.
There were times where jump couldn't be executed, especially downslope.
There was a video on how they achieved a really good responsive control, but I couldn't find it now.
One example is to give a short time buffer allowance for player to jump even if they are already off the platform.
Let the player blame themselves for losing, instead of blaming the game. :p
Oh ya, there's a bug where if you jump into the left hole, and keep falling left, you will miss the trigger somehow, and fading mechanic won't be applied to you.