I've noticed that the colors on the cat all look very nice together. The color combination would likely be impossible on a real cat, but I understand the color choice because it's a cross-over of two, which was done in a very creative way. I think his facial expression and the position he is standing in fit the character(s) very well.
One of the problems I see is that with the shading. I think you could benefit from trying to blend it a bit more; around the nose/mouth and near the shoulder it seems as though you hastily used just one brush.
The lightning is appealing visually, but you use very similar backgrounds in all of your drawings, and I believe it would look nice if you changed it up every once in a while; further, the plain gradient reminds me a bit of a website from the 90s, and really detracts from what could be a very powerful image of the cat.
What I see as the biggest flaw here is the anatomy. Frankly, it's very similar to that of a dog, which is a common mistake artists make when drawing cats. As a general rule, the body of a dog tapers off near the tail (which I see here), and a cat's body is shaped more like a bean. I suggest looking up a few images on cat anatomy to help you improve your technique.
Overall, the strongest points of the drawing, in my opinion, are the expression and position of the cat and the style in which you made this a cross-over, while you could use the most work in shading, background, and anatomy.
And I noticed the poor anatomy a few weeks after posting this. I've started paying more attention to the body structure of cats, especially their backbone. My main pet peeve with this drawing is how it looks like the tail is disconnected with his spinal bone. I see what you say in this critique is true, And I'm trying to improve.