The spirit shifting mechanic is really well done! once i saw that there's extra mechanics like your body floating slowly while in spirit mode, and the momentum you get from rejoining your spirit this movement really opened up!
There's a lot of play to this movement system and your level design really allows for people who grok the mechanics to soar through them and sequence break them which i find rewarding.
However, you've also made sure to introduce levels in an order that subtly teaches the player these more advance mechanics, so great level design and difficulty progression!