Good stuff, feels like a solid game!

You've got a nice and consistent art-style, interesting and challenging level-design and an easy to grasp but hard to master gameplay.
I could see myself quite invested in this game, if I wouldn't constantly slip or miss platforms xD

The shift ability is pretty neat and an interesting take on the theme.
Though it still handles player death the same way as your usual platformer; enemies and falling off the level.
Would love to see the theme be expanded to these areas, e.g. an actual "realm shift" when you die falling like an upside-down version of the level (inverted gravity?).

But honestly, it's a nice game on it's own and kudos for how quickly you pushed this out!

Really like the monochrome pixel art style, The gameplay was fun and challenging and the realm feature was easy to understand. It may have been better to have the realm switching possible with the keyboard as the mouse served no other purpose than to switch realms.

Other than that, the only real problem that I had was that the music was only playing out the left side of my headphones. Otherwise it was really good