Thanks for your feedback!
Most of the art isn't mine, but from this tileset. I've added the gatekeeper, the portal, the spikes, the additional wall tiles and some other bits.
With the dust effect do you mean you would use it for timing so that you can know when you can jump again immediately after landing? Because you autojump as long as you keep the jump button pressed.
The fourth mine is the nightmare mine; I'm planning it to be optional. I'm still thinking on how to set up the main game campaign.