Find That Book

There was a book I read some ten years ago in elementary school. I can't remember too much but for a few concrete details and a few things I'm not sure if I remember correctly. I have been unable to find this book and it's driving me half mad. I am hoping someone here can help?

Things I remember for certain:
It was a large paperback picture book.
A boy and his cat are on an adventure, looking for something.
They fail in their quest, so the king/monarch/ruler traps them each in a locked cube of sorts. (There's a happy ending eventually, I just don't remember how).
The illustrations are full of puzzles and illusions. There are two that I remember distinctly:
1. Towards the beginning, there was a full page illustration and the reader was supposed to find all of the cats. Some we actual cats, others were bushes or shadows or silhouettes made up of other objects.
2. A tunnel stretching out, with the lines along the wall getting closer together toward the far end. It was on of those height illusions, where all three objects were really the same size, but the lines made some appear larger than others.
Illusion and magic were major themes.

Things I may or may not remember correctly:
The cat was black or black and white
The boy wore an cloak that was somewhere on the red-orange end of the color spectrum and a pointed hat.
The boy and cat were trapped in separate magical cubes.
The ruler who had imprisoned them was deeply saddened by something.
The boy was a magician, or training to be one.
Many far more skilled magicians had attempted the quest before and all had failed and been imprisoned.
The objects in the tunnel height illusion mentioned above were toy beings of some sort--maybe toy soldiers?
The tunnel was a blue color and the height illusion objects seemed to be floating at different heights.
There was a large cat-shaped bush in the 'how many cats' illusion, and the caption for that image said something about being distracted and needing to find the boy's cat before moving on.
All the illustrations had a bit of fuzziness to them, like they had been originally done in colored pencil, but I might be making that up.

I can't remember anything else--it's been years since I had read it, but I remember it fondly. I would love to rediscover it, and would be so, so grateful to anyone who could provide me with a solid lead!