Sulphur Nimbus: Hel’s Elixir by Oddwarg

You are Sulphur Nimbus, a hippogriff who gets stuck on a cursed island during a sidequest gone wrong. Collect magical blobs, fight weird monsters, and get lost in the depths of the earth.
You’ll be able to fly wherever you want, but you’re a horsebird so it won’t be easy. As you dive deeper into the island’s underground caverns, you must learn to manage your momentum with increasing care and precision.
Sulphur Nimbus: Hel’s Elixir takes inspiration from momentum-based platformers, six-degrees-of-freedom games, action adventures and collectathons.
The project was funded on Kickstarter in 2016. (It took a bit too long to finish.) The source code is available on SourceForge. The original soundtrack is available on Bandcamp. If you are having trouble, or would like to discuss something else, there is a Discord server.
This game is known to cause motion sickness in some individuals, and has a steep learning curve.