Spoiler:
You need an extra cat. There is one in the preceding room, but you don't have enough movement. If you've opened the wormhole in 7,17 then you already have what you need. If you haven't, then you've got some other puzzles to solve first.
Then stack the cats and rocks so that you have the rocks above and below the flag, one cat on the flag, and one cat above. Then go straight down.
That's exactly what it seems to be. Just getting the cats requires solving a puzzle for each one. Getting a lot of the stars requires solving a chain of puzzles. And the secrets require.... a bit of lateral thinking would be an understatement. There's a reason I called the developer an evil genius somewhere in this comment section. The puzzle chains are brilliant.
If you're still working on 6,16, you won't be able to do that until you've unlocked the portals at 7,16. Those don't necessarily require that you got the star from 9,14 - but if you do have to start there, and having gotten the star will give you a very strong clue about how to start. (not that unlocking the portals is part of solving 6,16 - just that it will happen naturally on the way, and will make it easier to come back later)
Yeah, I've gone back through that one a couple times (because I forgot which portal would get me back to that room) and I have to figure it out again every time. But I think I've optimized it now.
To get past the top medusas, keep the cats as far apart as you can for the first two steps:
For the bottom medusas, the easiest thing to do is hold back two of the cats by the blue flags, send the first cat through. Push the left medusa down. Then jump on the spikes. Send the second cat the same way. Third cat pushes the middle medusa down.
