I was pleasantly surprised to find out that your secret project was a 3D game, and I'm impressed. It's pretty fun! I really like the movement options of being able to double jump and then roll in the air. A suggestion I have to make the movement options even more dynamic is that it would be cool if each jump resets your roll. So you can roll to jump to roll to jump to roll. That would add even more depth to the movement options and lead to more challenging platforming opportunities. As for the jumping mechanics, it feels kind of hard to jump the same height consistently, especially since jumping right next to a wall lowers your jump height (took me a while to figure out that was the main reason my jumps were inconsistent.) I also noticed that you have to hold the space bar a long time to jump high enough to get over most obstacles, which felt a little unnatural to me.
I thought the selfie feature with Alley was pretty clever, it made me laugh. Would be interesting in seeing more ways that the synergy of Pumk and Alley could lead to unique gameplay. For example, maybe if you grab Alley and throw her down below you it could give you an extra jump. Or Alley's camera could have a flash that could stun enemies for a second if they are looking in the direction of the camera. I haven't read Bail Jape yet so forgive me if my suggestions don't fit the themes of the characters.
Some other notes: I wish you could move the camera higher above because sometimes you cannot see fairy bits that are above you. Also, I'm sure you would like to know information about how many fairy bits each player collects, so I can tell you I played for almost an hour an collected around 230. I have no idea how to get these fairy bits on a platform near the starting area. I usually am not the type of person to collect everything in 3d platformers and am satisfied with casually exploring the level so I'm going to call it there.
All in all, great demo, and I'm looking forward to the future of this project!