Thanks for playing! There are, in fact, a couple of hidden rooms within the first area that just contain wood for bowls, but we might have to revise the sprite for the "hidden room wall" tiles, as it seems a lot of people keep missing them.
As for the waterfalls, I actually thought about that too, and we might make something like a blinking border in order to make it more obvious for the player that they are freezable.
As for the controls, we might actually add some kind of telegraph for where the potions are gonna go when you throw them, since you're not the first one to point that out, either that or we increase the bats' hurtbox. And about the button ordering thing... I honestly forgot I added bindings for zxc, which is probably why the distribution feels so weird haha. It is explained in game that the button to switch between potions is 'O', although I think I can see how it might be hard to miss.
Anyway, thanks for the feedback! I'll be noting some of these down in the "Known issues" section of the game's page :)