What part of it are you stuck on? I'm assuming you've already figured out the in-game hint about wormholes and just don't know how to get around the medusas while making sure to have enough cats to replace the stone reach all wormholes?
The splitters will get you there. Remember the splitters don't change the direction you face, so horizontal splitter to "back up" onto the vertical splitter. From there clone cats to your heart's content. You'll need three. If you're not careful you'll get a lot more, and it'll be really hard to navigate.
Is there a way to beat the level even normally without getting rid of two medusas? Because you only need to get rid of two of them. But if you managed to somehow beat the level without doing that before then here's what you need:
Top rock right of horizontal splitter. That's basically it. Now you can destroy two medusas using the other rock in order to get the timing right. From there, it's all about working the splitters to get more cats facing right until you have enough to finish the level.
Edit: Actually, looking back now, I can't even remember how to beat it without cloning cats, so there must have been a way I don't remember that didn't kill the medusas. Honestly, I think the "secret" solution is easier now.
If you now have this:
| Medusa | V-Splitter | H-splitter | Rock |
| Medusa | V-Splitter | Rock | |
| Wall | Flag | Cat |
Then up followed by left will clear the first rock and give you a fresh cat. After that you can use the H-Splitter->V-Splitter to duplicate the cat.
I misremembered though - you only need one extra cat. I thought I had to replace the destroyed rock, but I didn't have to.
You do!?? Congrats. I'm still missing two cryptids. I just went back over (I think) every room last night (although I didn't check them off on a grid or anything as I went, I probably should have), and I don't see *any* room that has a wormhole I haven't activated or where I can "break" an exit that I haven't already.